[coreboot] [v3][patch] Add AP detection to stage0

[Marc Jones]

Add AP detection to stage0 to prevent APs from re-initializing mainboard setup
that has already been done by the BSP. For single processor systems the CPU
flag is always 0, BSP. This code also moves the AP stop for K8 mainboards to
after memory setup so the AP's MTRRs can be setup to match system memory.

Signed-off-by: Marc Jones