spec_fpga_app_init() declares too many local buffers that are allocated on the stack.

On some versions of GCC this is detected and reported, causing a warning that is promoted to an
error. Example:

spec-core-fpga.c:792:1: error: the frame size of 1888 bytes is larger than 1024 bytes
[-Werror=frame-larger-than=]

Since apparently it is not a very good idea to increase the stack frame size limit [1], the solution
implemented here is to switch to dynimically allocating the biggest buffer (struct resource res[]).

[1]: https://gcc.gnu.org/onlinedocs/gccint/Stack-Checking.html#Stack-Checking
"The maximum size of a stack frame, in bytes. GCC will generate probe instructions in non-leaf
functions to ensure at least this many bytes of stack are available. If a stack frame is larger than
this size, stack checking will not be reliable and GCC will issue a warning. The default is chosen
so that GCC only generates one instruction on most systems. You should normally not change the
default value of this macro."
Signed-off-by: Dimitris Lampridis <dimitris.lampridis@cern.ch>