Ben H added a check in a couple of places to make sure that we had
preemption disabled when we call enable_kernel_{fp,altivec}.
Unfortunately the check he used trips in the case when
CONFIG_PREEMPT=n.  This patch fixes it by defining a preemptible()
macro (which reduces to 0 when CONFIG_PREEMPT=n) and doing
WARN_ON(preemptible()).
Signed-off-by: Paul Mackerras <paulus@samba.org>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>