soc: intel_adsp: only implement FW_STATUS boot protocol for cavs

The software protocol to write status value of 0x05 (FW_ENTERED)
into memory window 0 at Zephyr boot, is not needed in the ace1.x
boot flow and does not match the semantics host systems are expecting
at this location in the memory window (e.g. write of 0x05 is not
expected).

Make this logic specific to intel_adsp_cavs platforms and move the code
out from common intel_adsp code.

This commit depends on update to cavstool.py to use correct
ROM status register to observe boot state.

Signed-off-by: Kai Vehmanen <kai.vehmanen@linux.intel.com>