drm: atmel-hlcdc: support extended timing ranges on sama5d4 and sama5d2

The display timings on old SoCs older than the sama5d4 are quite limited
and prevent the use of many displays. Add support for extended timing
ranges on sama5d2 and sama5d4.

Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Tested-by: Nicolas Ferre <nicolas.ferre@atmel.com>