[ARM] 4234/1: Introduce get_irqnr_preamble and arch_ret_to_user for ns9xxx.

This is a follow up for f80dff9d which
didn't include adaption for the new ns9xxx machine support.

Signed-off-by: Uwe Kleine-König <ukleinek@informatik.uni-freiburg.de>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>