ARM: v6k: remove CPU_32v6K dependencies in asm/spinlock.h

SMP requires at least the ARMv6K extensions to be present, so if we're
running on SMP, the WFE and SEV instructions must be available.

However, when we run on UP, the v6K extensions may not be available,
and so we don't want WFE/SEV to be in the instruction stream.  Use the
SMP alternatives infrastructure to replace these instructions with NOPs
if we build for SMP but run on UP.

Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>