Only BSP CPU writes CMOS in bootblock code

Only BSP CPU writes CMOS in bootblock code

CMOS accesses are not safe for multi-processor and only the BSP CPU
should count reboots and test CMOS sanity.

A questionable single byte CMOS read access from AP CPUs remains.
AP CPUs should always select the same romstage prefix as BSP CPU.

Change-Id: I29118e33c07c0080c94abb90f703e38312c72432
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/446
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>