drm/msm/dsi-staging: add debugfs support to switch panel esd check mode

Panel ESD check mode is statically defined in device tree.
This change adds support to dynamically alter this mode from
debugfs node.

For example, the debugfs node for ESD check mode will be
available at /<debugfs-root>/<active display>/esd_check_mode

Commands for altering ESD check mode:

For register read based ESD check:
"echo reg_read> /d/dsi_nt35597_truly_dsc_cmd_display/esd_check_mode"
For panel TE based ESD check:
"echo te_signal_check> /d/dsi_nt35597_truly_dsc_cmd_display/esd_check_mode"

Change-Id: I6f8fbe180c1068d09acb9a5b8696c372ac19df9b
Signed-off-by: Shashank Babu Chinta Venkata <sbchin@codeaurora.org>