ARM: dts: exynos5420: remove disp_pd

This was caused by commit 5a8da524 ("ARM: dts: exynos5420: add dsi
node"), which conflicted with d51cad7d

 ("ARM: dts: remove display
power domain for exynos5420").

The DTS addition should never have been merged through the DRM tree in
the first place, and it lacked an ack from the platform maintainer
(who would have known that the disp_pd reference got removed).

Signed-off-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Olof Johansson <olof@lixom.net>