drm/msm/dsi-staging: add support for overlap pixels in dsi driver

In foldable phones, panels show extra overlap pixels data per dsi.
Due to which the effective width of the panel per dsi becomes
actual width in pixels plus size of overlap pixels. This change
adds support in dsi driver for overlap pixels used in foldable phones.

Change-Id: Ic9dbf3db9fe3e301fa12c198c6d34ce2de08b5e8
Signed-off-by: Sandeep Panda <spanda@codeaurora.org>
Signed-off-by: Tharun Raj Soma <tsoma@codeaurora.org>