[ARM] Fix kernel-mode undefined instruction aborts

If the kernel attempts to execute a CP1 or CP2 instruction and it
aborts, and a FP emulator is not loaded, we try to return as if to
a user context, instead of the proper kernel context.  Since the
fault came from kernel mode, we must use the kernel return paths.

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