Small SMM fixups

Small SMM fixups

Align the spinlock to the 4 byte boundary (CPU will guarantee atomicity of XCHG).
While at it add the PAUSE instruction to spinlock loop to hint the CPU we are just
spinlocking. The rep nop could not be used because "as" complains that rep is used
without string instructions.

Change-Id: I325cd83de3a6557b1bee6758bc151bc81e874f8c
Signed-off-by: Rudolf Marek <r.marek@assembler.cz>
Reviewed-on: http://review.coreboot.org/81
Tested-by: build bot (Jenkins)
Reviewed-by: Patrick Georgi <patrick@georgi-clan.de>