MLK-16906: drm: imx: core: add possiblity to detect if chip has DCSS

MLK-16906: drm: imx: core: add possiblity to detect if chip has DCSS

The Mscale Display Controller Subsystem does not support RGB565.
However, the default legacy FB pixel depth is 16. Hence, the users would
have to add a kernel cmdline option to set it to 32bpp:
imxdrm.legacyfb_depth=32

This patch changes imx-drm-core to detect if platform has DCSS and, if
it does, set the FB pixel depth to 32, so that user does not have to.

Signed-off-by: Laurentiu Palcu <laurentiu.palcu@nxp.com>