Use the generics for memory insted of infererence.
Also, remove read-during-write bypass by tweaking index comparisons.

We cannot access variables outside the process, which we will need
to be able to do in the next patch.

The optimizer should be able to remove all the control registers
as they are unchanging, so nothing is lost.

On slow Wishbone slave devices (eg. flash), the next request might
be decoded by the PHY before first has exited the read_first state.
In this case, the bar could change causing the mux to prematurely
lower the stall line.

The LM32 needs a read-enable.
Unfortunately, Xilinx does not have one, so we emulate it.

By using altsyncram directly, we get the follow benefits:
  * clear control of read-write resolution behaviour
  * can specify a mif file for initialization
  * eliminates warnings about dual-port clock inference timings

On Altera, "" generates a null-range warning.
When the dpram is used heavily, these warnings add up to many.

The RW ordering on address conflict varies by platform.
Some platforms only support some options.
Most of the dprams in WR are portable and don't depend on the order.
This new option allows a core to specify that it does not care what
the result of a RW conflict is, and thus work on more platforms.

For Xilinx, "dont_care" = "read_first", the old default.

On both Altera and Xilinx, a dual port memory can achieve twice the
bit-width per memory block when there is a single reader and writer.
This adds a place-holder generic_simple_dpram for Xilinx so that code
using the purpose-built variant for Altera continues to work on ISE.

In the past we used a generic to set the initial memory contents on altera.
Unfortunately, quartus compiles big generics slowly (read: hours).
Now we can load from a .mif file instead, which is much faster (seconds).
Thus, this old option is no longer needed.

There were many constructs like this:
  gen_with_empty : if(g_with_empty) generate
    empty_o <= empty;
  end generate gen_with_empty;

If g_with_empty is true, then there are no warnings.
If g_with_empty is false, then empty_o is unset and empty is unused.

There is no improvement in performance/resource utilization to explicitly
cutting these signals. The optimizer will happily discard unused logic.

The alternative of adding
  gen_without_empty : if(not g_with_empty) generate
    empty_o <= 'X';
  end generate gen_without_empty;
will remove the empty_o unset warning, but not the empty unused warning.

This patch does make it possible for designs to  use empty_o without
setting g_with_empty; an error. On the other hand, those designs had
undefined behaviour before anyway, so they might have worked unreliably.

CFG_EBA_RESET is supposed to be the default value of the LM32's eba_reset
parameter. Unfortunately, the constant leaked into the sources directly.

In order to clean-up a truncation warning for pc_f, it was easiest to fix
the missing parameter and then use a subarray of that value.

Some signals are flat-out unused
 => these are outright removed
Some signals are used only under certain conditions
 => these have the definitions made also conditional

In Verilog, an "assign x = y;" will cause a warning in Quartus if x was not defined.
For example,
  Warning (10236): Verilog HDL Implicit Net warning at lm32_allprofiles.v(45398): created implicit net for "multiply"
This patch defines all such nets.

Also, the CSR width is too narrow by default (CFG2 must fit).