drm: omapdrm: Infer the OMAP version from the SoC family

The omapdrm exposes the SoC version to userspace through an integer that
contains the OMAP model (e.g. 0x3430 for the OMAP3430). This is an
unfortunate choice of userspace API as it's both conceptually wrong
(userspace nowadays should use /sys/bus/soc/ for that purpose) and
inaccurate as many models with different features are reported with the
same version number.

The only known user of this API is the xomap X11 driver. Even if it has
been deprecated for some time we can't drop the kernel API yet. We can,
however, infer the version number from the SoC family to avoid the need
to pass the version number through platform data.

Do this, which makes the omapdrm platform data not needed anymore, and
ready to be removed.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>