disp: msm: dsi: add debug ability to read TE read pointer line count

The change adds register mapping of MDP_INTF_[1/2]_TEAR_INT_COUNT_VAL
register to DSI controller. This allows for the controller to read the
line count and frame count of the read pointer during trigger and
successful transfer of DMA command.

To enable the debug feature:
echo 1 > /d/<panel_name>/dsi-ctrl-0/enable_cmd_dma_stats.

To disable the debug feature
echo 0 > /d/<panel_name>/dsi-ctrl-0/enable_cmd_dma_stats.

To read line count value:
cat /d/<panel_name>/dsi-ctrl-0/cmd_dma_stats.

Change-Id: I5cdeb54ca941af05b226a9d7ab332b899ecc5797
Signed-off-by: Satya Rama Aditya Pinapala <psraditya30@codeaurora.org>