msm: mdss: program gamut registers only if offset present

Gamut may not be present in all targets. The device tree
offset for gamut can indicate presence of block on target.
Program gamut if gamut offset is present in mdss device
tree. Also allow parsing of further PP block offsets in
device tree even when gamut entry is absent.

Change-Id: I87d057190dcfdb3cb57d88ea3b6d68f02deac5fa
Signed-off-by: Krishna Chaitanya Parimi <cparimi@codeaurora.org>