spi: Add MXIC controller driver

Add a driver for Macronix SPI controller IP.

This patch referred from linux spi-mxic.c. The difference from the
linux version is described here.

1. To adapt uboot spi framework, modify some functions naming.

2. Remove the incompatible functions of Uboot.

3. Add dummy byte recalculattion function to support dummy buswidth
   not align data buswidth operation.(ex: 1-1-4, 1-1-8)

4. Add Octal mode support.

Signed-off-by: Zhengxun <zhengxunli.mxic@gmail.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>
[jagan: fixed file permission, comment line, kconfig]
Signed-off-by: Jagan Teki <jagan@amarulasolutions.com>