memory: omap-gpmc: Add support for AAD timings

In order to support extended timings parameters on hardware supporting the
"AAD" mode like the AM335x or DM816x, add these entries into the GPMC driver
if the hardware is capable.

Tested on DM816x and AM335x.

Signed-off-by: Neil Armstrong <narmstrong@baylibre.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Roger Quadros <rogerq@ti.com>