ARM: dts: msm: Add idle-fps entry for auo 390 panel

Add idle-fps value for auo 390 panel for 8909
targets which indicates the panel framerate in
idle mode.

Change-Id: I48eec357a5ee4dfc10950253fb5e75ce8e01fd6f
Signed-off-by: Krishna Manikandan <mkrishn@codeaurora.org>
Signed-off-by: Abhijith Desai <desaia@codeaurora.org>