drm/msm/sde: add sde debug bus dump support

Add support for dumping the sde and vbif debug buses. Can be
triggered via sysfs, or via the SDE_DBG_DUMP macros by providing
"dbg_bus" or "vbif_dbg_bus" strings in the dump area list.

Change-Id: I8b3261a7bdc0161e77729ed0d05bf90cf9214298
Signed-off-by: Lloyd Atkinson <latkinso@codeaurora.org>