media: sunxi: Depend on GENERIC_PHY_MIPI_DPHY

The sun6i-mipi-csi2 and sun6i-a83t-mipi-csi2 drivers depend on the generic
MIPI D-PHY support. Select it. This fixes a linking problem when either of
these drivers is enabled and GENERIC_PHY_MIPI_DPHY is disabled.

Signed-off-by: Sakari Ailus <sakari.ailus@linux.intel.com>
Reviewed-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>