drm: atmel-hlcdc: add sam9x60 LCD controller

Add the LCD controller for SAM9X60.

Signed-off-by: Sandeep Sheriker Mallikarjun <sandeepsheriker.mallikarjun@microchip.com>
[claudiu.beznea@microchip.com: add fixed_clksrc option to
 atmel_hlcdc_dc_sam9x60]
Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/1556195748-11106-6-git-send-email-claudiu.beznea@microchip.com