ARM: 5883/1: Revert "disable NX support for OABI-supporting kernels"

This reverts commit 14f0aa359365e8a93a77b71e3b840274b9b4dcb1.

That commit was needed earlier because system call restarting for
OABI (compat) required an executable stack and thus had problems
with NX.  Since ab72b00734ae4d0b ("ARM: Fix signal restart issues
with NX and OABI compat") has reworked the code to not require an
executable stack anymore, we can re-enable NX support for kernels
with OABI (compat) support.

Signed-off-by: Rabin Vincent <rabin@rab.in>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>