firmware: shmbridge: Enable shmbridge by default

The SCM driver depends on shmbridge to make calls to the TZ. This
change enables shmbridge by default if CONFIG_QCOM_SCM is set.

Change-Id: I56a2cf35d5621f9b7ca4e8b3e854671e8d40071c
Signed-off-by: Siddharth Gupta <sidgup@codeaurora.org>