ARM: dts: msm: remove mdss gdsc entry for sm6150

This change removes the mdss core gdsc entry from mdss_mdp
node when display RSC is enabled. Display RSC hardware will
enable/disable the mdss core gdsc, so there is no need for
driver to control it.

Change-Id: Ie881e1d5312edc36989edca55d54430273531133
Signed-off-by: Abhijit Kulkarni <kabhijit@codeaurora.org>