msm: smd_debug: convert to sequential file system

smd_debug uses a 4k buffer for outputting information to debugfs.  Some of
the debugfs output exceeds 4k in size, resulting in truncated output.  The
sequential file system framework is an alternative to this 4k buffer and
has no practical size limitation.

Replace the 4k buffer with sequential files to prevent truncated output.

Change-Id: I744075f7b71264c5d59bcee714afa6d5f180b436
Signed-off-by: Jeffrey Hugo <jhugo@codeaurora.org>