ARM: davinci: dm644x-evm: use aemif platform driver

We now support board files in the aemif driver. Register a platform
device instead of using the handcrafted API in dm644x-evm.

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>