drm/msm/sde: Add global dither memory dump range

The global dither memory range can not be accessed from outside.
So the patch fixs this issue through add global dither memory range
to valid range.

Change-Id: I3ab5b87ff1e62f7b19b48a137922d4e98a64040c
Signed-off-by: Yuchao Ma <yuchaom@codeaurora.org>