`hw version` and `hw status` decoded the reported chip id as an Atmel AT91
CIDR. On PM5 (AT32) the id is an ARM DBGMCU IDCODE, so it showed
"MCU Unknown", a bogus flash size (32 KB / 973% used) and "PM3 GENERIC".
- Client: when IfPm5(), print MCU "AT32F437" and the real flash size, and add
a "PM5" target line, instead of running the AT91 decode.
- Firmware: the flash size can't be derived from the AT32 IDCODE, so the device
now sends GetChipFlashSize(). It is appended AFTER the version string in the
CMD_VERSION reply, so the wire layout is unchanged and it stays compatible in
both directions (old client ignores the trailing bytes; new client length-
guards and treats a missing value as 0). GetChipFlashSize() already exists for
both AT91 and AT32.
Also allow flash to be separately enabled via PLATFORM_EXTRAS.
NOTE: this does *NOT* enable the serial number
in the bootrom. Still investigating options there.
Nemanja Nedeljkovic