soc: qcom: ssr: Add subsys_set_error API

Adding a new API subsys_set_error() which can indicate reason why a
subsystem failed to come up. This error reason can be useful for some
userspace helper application to take appropriate action.

Change-Id: I6df3580befd48a6b83bb8fd1099475da42fc9cf2
Signed-off-by: Meghana Ashok <meghanaa@codeaurora.org>