media: nxp: Restrict VIDEO_IMX_MIPI_CSIS to ARCH_MXC or COMPILE_TEST

The imx-mipi-csis driver is specific to NXP platforms. Restrict it to
those by default, and enable compilation with COMPILE_TEST to keep a
wide test coverage.

Link: https://lore.kernel.org/linux-media/20220318203735.5923-1-laurent.pinchart+renesas@ideasonboard.com
Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Rui Miguel Silva <rmfrfs@gmail.com>
Reviewed-by: Kieran Bingham <kieran.bingham+renesas@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>