ARM64: dts: meson-gxm: Rename q200 and q201 DT files for consistency

In order to keep consistency naming with the Nexbox A1 DTS file, remove the
S912 SoC name in the GXM DT files.

Suggested-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Signed-off-by: Kevin Hilman <khilman@baylibre.com>