This commit does three changes to gc_sync_word_wr:

1. It converts it to use internally gc_pulse_synchroniser2
2. It introduces a new "busy" output bit
3. It introduces a new generic, g_AUTO_WR which instructs the core to write a new word continously, without input from the user.

When trying to compile for nanoXplore synthesis fails, complaining
about those signals -- although they're unused.

This is needed for fixed-latency streamers. Module was written by Tom,
he added it to wr-cores whereas it belongs here, I've moved it.

This is beneficial because the gc_sync_ffs has a Xilinx "keep" attribute, which prevents the tools
from trimming out unused logic, even when the user has set the relevant generics to "FALSE".

genrams: when pre-loading a RAM with an init file, assert that the file size is not bigger than the size of the memory it is written to

genrams: when pre-loading a RAM with an init file, assert that the file size is not bigger than the size of the memory it is written to