msm: mdp: allow overriding of splash_screen_size

Change-Id: I7705c16e5ca1f147d3ca647d02af25136f32b0ab
monarudo: update display boardfile

* enable splash screen and set splash_screen_size
* reduce minimum brightness

Change-Id: I6f321d585e9ef428f62139c2c678b12fbb22f900