slim_msm: Report flow-error and mask apps slimbus port interrupts

Apps side slimbus ports may overflow/underflow if BAM pipes connected
to those ports don't have descriptors scheduled.
Report such errors and mask the port interrupts until BAM pipes have
descriptors scheduled to avoid interrupts firing multiple times.

Change-Id: I4a2bf716ad0a9ee4f71c4ee36b84826b9d90e3b8
Signed-off-by: Sagar Dharia <sdharia@codeaurora.org>