gc_frequency_meter: use gc_pulse_synchronizer for external PPS pulse (in case the measured frequency is slower than the gating frequency)

0 is impossible, since it is the interconnect record
=> use it instead

The subrange type might not be known in this context.
Fixes:
  wishbone_pkg.vhd:1379:26: object subtype is not locally static

Variable lengths might change; standard forbids length in a loop.
Fixes:
  wishbone_pkg.vhd:1576:18: universal integer bound must be numeric literal or attribute
  wishbone_pkg.vhd:1613:18: universal integer bound must be numeric literal or attribute
  wishbone_pkg.vhd:1734:30: universal integer bound must be numeric literal or attribute
  wishbone_pkg.vhd:1771:16: universal integer bound must be numeric literal or attribute
  wishbone_pkg.vhd:1806:16: universal integer bound must be numeric literal or attribute
  wishbone_pkg.vhd:1817:16: universal integer bound must be numeric literal or attribute

The so-called "inferred_X_fifo" are basically generics fifos using
inferred rams blocks from altera or xilinx, depending the target
platform. That's why it makes more sense to move them to the "generic"
folder of genrams. This change forces to rename the "generic_X_fifo"
under "altera". Since these fifos are using the altera fifo  Megafunction,
are going to be called "altera_X_fifo". The Manifest has been changed accordingly.