ramips: second spi device on rt5350

ramips: second spi device on rt5350

This is based on Jon Smirl's patch with the following changes:
- Set CS polarity as low by default.
- Add support for changing CS polarity.
- Add support for changing LSB/MSB.
- Add support for changing SPI mode.
- Fix indentations.

I tested it on a VoCore. Works fine connected to a second flash, but fails to detect MMC/SD cards due to SPI clock speed.

Signed-off-by: Jon Smirl <jonsmirl@gmail.com>
Signed-off-by: Álvaro Fernández Rojas <noltari@gmail.com>
Backport of r42276

git-svn-id: svn://svn.openwrt.org/openwrt/branches/barrier_breaker@42375 3c298f89-4303-0410-b956-a3cf2f4a3e73