arm: fiq: Provide empty stubs for fiq functions

A driver using fiq functions should be usable on targets
with or without CONFIG_FIQ enabled. Instead of making code
dependent on #ifdef CONFIG_FIQ, add empty stubs for the fiq
functions.

Change-Id: Ie8b1905ba53664d99bd707be3c83291c97eb1066
Signed-off-by: Rohit Vaswani <rvaswani@codeaurora.org>
(cherry picked from commit eb81fb3bdea411fed5c26400f9769bad7fb0743f)