msm: sps: Add debugfs support for IPC logging in SPS driver

IPC logging for SPS driver, helps monitoring the interactions
between BAM clients and SPS driver and helps tracking the BAM
status. Add debugfs support such that clients can specify the
loglevel at runtime for IPC logging through debugfs.

Change-Id: Ie5b833a211c8decdcc8c41c376a2adc07ab4ba65
Signed-off-by: Rama Krishna Phani A <rphani@codeaurora.org>