rockchip: px30: Add support for using SFC

This patch adds support for setting the correct pin configuration
for the Rockchip Serial Flash Controller found on the PX30.

Signed-off-by: Chris Morgan <macromorgan@hotmail.com>
Signed-off-by: Jon Lin <jon.lin@rock-chips.com>
Reviewed-by: Kever Yang <kever.yang@rock-chips.com>