drm/msm/sde: Add LTM histogram control support

This change adds support for LTM histogram control, including setting
up ION buffers for LTM histogram, configuring the histogram HW
and enable LTM histogram interrupts.

Change-Id: I44afaa8eb6efe339e1da604c9c5f7d0836def138
Signed-off-by: Ping Li <pingli@codeaurora.org>