drm/modes: Support modes names on the command line

The drm subsystem also uses the video= kernel parameter, and in the
documentation refers to the fbdev documentation for that parameter.

However, that documentation also says that instead of giving the mode using
its resolution we can also give a name. However, DRM doesn't handle that
case at the moment. Even though in most case it shouldn't make any
difference, it might be useful for analog modes, where different standards
might have the same resolution, but still have a few different parameters
that are not encoded in the modes (NTSC vs NTSC-J vs PAL-M for example).

Reviewed-by: Noralf Trønnes <noralf@tronnes.org>
Signed-off-by: Maxime Ripard <maxime.ripard@bootlin.com>
Link: https://patchwork.freedesktop.org/patch/msgid/18443e0c3bdbbd16cea4ec63bc7f2079b820b43b.1560783090.git-series.maxime.ripard@bootlin.com


Patch-mainline: 18443e0c3bdbbd16cea4ec63bc7f2079b820b43b.1560783090.git-series.maxime.ripard@bootlin.com @ 17/06/19, 02:51 p.m.
[stalek@codeaurora.org: drop changes for drm_modes.c as some of the existing code
changes are missing and the change is not require.].

Change-Id: I2250d71ac583332c60fd0c05be15cf20dfbcc0f6
Signed-off-by: Shubham Talekar <stalek@codeaurora.org>