MAINTAINERS: Remove tinydrm entry

tinydrm is just a collection of tiny drivers now.
Add T: drm-misc entry for tinydrm drivers that lacks it.

Cc: David Lechner <david@lechnology.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Signed-off-by: Noralf Trønnes <noralf@tronnes.org>
Acked-by: David Lechner <david@lechnology.com>
Acked-by: Eric Anholt <eric@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20190722104312.16184-10-noralf@tronnes.org