ARM: dts: mdss: Add boolean property for LUT readability

LUT read is not supported by hardware in the case of msm8226.
Adding property to dtsi file to denote the absense of support
for read in hardware.

Change-Id: I29cf869af4135e1199bc0feb4369700b994520ec
Signed-off-by: Krishna Chaitanya Parimi <cparimi@codeaurora.org>