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: I61bf00975ffac73c37f66dbc47dcc11b31df45df
Signed-off-by: Thomas (Wonyoung) Yun <wyun@codeaurora.org>