diag: Reorganize code to provide improved functional access

The diag kernel code has some large files that are
becoming unwieldly. Separate out existing debugfs and mask
related code into their own respective files to allow easier
functional access and reduce file size.

Change-Id: Ifde0963a3682f787dc892fb136d9d7d7ae1b7c01
Signed-off-by: Dixon Peterson <dixonp@codeaurora.org>