imx: mx6q: add aipstz init for off platform periph

Init peripheral access control register of AIPSTZ OPACRx:

Buffer Writes(BW):      0 -> not bufferable,
Supervisor Protect(SP): 0 -> not require supervisor privilege level for accesses.
Write Protect(WP):      0 -> allows write accesses.
Trusted Protect(TP):    0 -> allows unstrusted master

Signed-off-by: Jason Liu <jason.hui@linaro.org>
Cc: Stefano Babic <sbabic@denx.de>