ARM: dts: msm: assign virtual planes on msm8996 auto platform

The virtual planes are used to support wider HDMI display. Enable
them on msm8996 auto platforms in order to support 4K HDMI display.

Change-Id: I5deb5f5eaec25a495266175b188c6965a2dc9297
Signed-off-by: Jin Li <jinl@codeaurora.org>