memory: davinci: add support for da8xx DDR2/mDDR controller

Create a new driver for the da8xx DDR2/mDDR controller and implement
support for writing to the Peripheral Bus Burst Priority Register.

Reviewed-by: Kevin Hilman <khilman@baylibre.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
[nsekhar@ti.com: subject line adjustment]
Signed-off-by: Sekhar Nori <nsekhar@ti.com>