ARM: dts: imx6q-gw5xxx: remove dead 'crtcs' property

Since commit (655b43cc

 staging: imx-drm-core: Use OF graph to find
components and connections between encoder and crtcs), 'crtcs' becomes a
dead property.  Remove it.

Signed-off-by: Shawn Guo <shawn.guo@freescale.com>
Acked-by: Tim Harvey <tharvey@gateworks.com>