ARM: Ensure predictable endian state on signal handler entry

Ensure a predictable endian state when entering signal handlers.  This
avoids programs which use SETEND to momentarily switch their endian
state from having their signal handlers entered with an unpredictable
endian state.

Cc: <stable@kernel.org>
Acked-by: Dave Martin <dave.martin@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>