drm/sun4i: dsi: Add Allwinner A64 MIPI DSI support

The MIPI DSI controller in Allwinner A64 is similar to A33.

But unlike A33, A64 doesn't have DSI_SCLK gating so add compatible
for Allwinner A64 with uninitialized has_mod_clk driver.

Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>
Tested-by: Merlijn Wajer <merlijn@wizzup.org>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20191222132229.30276-6-jagan@amarulasolutions.com