More developments with BOOT

[Edw590]

The CPU is reading things from somewhere (I didn't get to check where
from, but instruction data is arriving) - but something's not right
because it doesn't try to write anything (wdata always xxxx) and preboot
tells the CPU to write the bootloader to memory.

List of changes:

• There are 2 SWRegs now, one for the CPU reset pulse and another one to
  store the current boot stage.
• Full ROM removed, and instead there are only the preboot and
  bootloader separate ROMs, and only the bootloader one goes into the
  ROM SWReg.
• Correction in concatenation order in iob_soc.v (was inverted).
• CPU pulse request created and possibly ready inside iob_soc_boot.v.