mailbox: imx: ONLY IPC MU needs IRQF_NO_SUSPEND flag

IPC MU has no power domain assigned and there could be IPC during
noirq suspend phase, so IRQF_NO_SUSPEND flag is needed for IPC MU.
However, for other MUs, they have power domain assigned and their
power will be turned off during noirq suspend phase, but with
IRQF_NO_SUSPEND set, their interrupts are NOT disabled even after
their power turned off, it will cause system crash when mailbox
driver trys to handle pending interrupts but the MU power is already
turned off.

So, IRQF_NO_SUSPEND flag should ONLY be added to IPC MU which has
power domain managed by SCU, then all other MUs' pending interrupts
after noirq suspend phase will be handled after system resume.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Jassi Brar <jaswinder.singh@linaro.org>