msm: mdss: Adding Source Histogram implementation

Source side histogram start/stop requests can be enabled through Overlay
API, and collected through MSMFB_HISTOGRAM ioctl. All requests take
updated 'block' parameter that lets multiple pipes be configured at once
to simplify userspace post processing calls in dual pipe case.

Change-Id: Ib2b8f4f8e2ec864e774f34a0b788a9949ce7513d
Signed-off-by: Carl Vanderlip <carlv@codeaurora.org>