board:origen: Enable device tree on Origen

This patch enables to run Origen board on device tree.

Uart, DRAM and MMC init functions are removed as their
generic replacements form the common board file are used.

The config file is modified to contain only board specific options.

Signed-off-by: Piotr Wilczek <p.wilczek@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Cc: Chander Kashyap <k.chander@samsung.com>
Signed-off-by: Minkyu Kang <mk7.kang@samsung.com>