drm/modes: Don't apply cmdline's rotation if it wasn't specified

Taken from the dri-devel mailing list (11/7/2019) to fixup the cmdline
parsing, but requires changes as things have moved between 4.19 and 5.2.

From: Dmitry Osipenko <digetx@gmail.com>

The rotation mode from cmdline shouldn't be taken into account if it
wasn't specified in the cmdline. This fixes ignored default display
orientation when display mode is given using cmdline without the
rotation being specified.

Fixes: 1bf4e092

 ("drm/modes: Allow to specify rotation and reflection on the commandline")
Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Signed-off-by: Dave Stevenson <dave.stevenson@raspberrypi.org>