disp: msm: dsi: parse & store gpio registers used by the host & panel

Parse all the GPIO pins used by the DSI host and the display panel
along with its register ranges and store it in panel struct. This
avoids parsing the device-tree everytime during transitions between
trusted and primary vm.

Change-Id: Ibbb646358c0409703afda1c4f758f044fc8c0001
Signed-off-by: Veera Sundaram Sankaran <veeras@codeaurora.org>