rockchip: px30: add support for SFC for Odroid Go Advance

The Odroid Go Advance uses a Rockchip Serial Flash Controller with an
XT25F128B SPI NOR flash chip. This adds support for both. Note that
while both the controller and chip support quad mode, only two lines
are connected to the chip. Changing the pinctrl to bus2 and setting tx
and rx lines to 2 for this reason.

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>