ARM: dts: msm: include mdss devices in msm8994 dtsi file

Include the msm8994 specific mdss dtsi file so that mdss
devices get enabled for this target.

Change-Id: I40a36754d88c723630cb27613a2d1472e840061a
Signed-off-by: Chandan Uddaraju <chandanu@codeaurora.org>