msm: modem-ssr-8974: Introduce a modem SSR driver for the 8974

The modem on the 8974 notifies the krait subsystem of a
fatal error via an SMSM interrupt or a watchdog-triggered
interrupt. Introduce a driver that monitors the SMSM
state and the modem watchdog bite interrupt line and
restarts the modem or the target when they are triggered.

Change-Id: I4291be11d33f99839b98da484e105e0a59a53e21
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>