Bootblock does not need a unique boot_cpu()

Bootblock does not need a unique boot_cpu()

Detection of a CPU being a BSP CPU is not dependent of the existence
of northbridge and/or southbridge init code in the bootblock.

Even if CONFIG_LOGICAL_CPUS==0, boot_cpu() can get executed on an AP
CPU of a hyper-threading CPU and needs to return actual BSP bit from
MSR.

Change-Id: I9187f954bb357ba1dbd459cfe11cc96cb7567968
Signed-off-by: Kyösti Mälkki <kyosti.malkki@gmail.com>
Reviewed-on: http://review.coreboot.org/447
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>