msm: mdm: Add support for remote MDM image upgrade

mdm-driver is informed that an image upgrade of the remote modem is
required, at which point it stops monitoring the error gpios and takes
the appropriate actions. Support for the "USB Switch" gpio is added.
This is needed to write a image to an empty modem flash.

Change-Id: I4c05a80955124a3eb7edc11e99f4945f9de79e6b
Signed-off-by: Ameya Thakur <ameyat@codeaurora.org>