New i.MX31 SPI driver

This is an SPI driver for i.MX and MXC based SoCs from Freescale. So far
only implemented and tested on i.MX31, can with a modified register layout
and definitions be used for i.MX27, I think, MXC CPUs have similar SPI
controllers too.

Signed-off-by: Guennadi Liakhovetski <lg@denx.de>
diff --git a/README b/README
index 3a10bd7..956c694 100644
--- a/README
+++ b/README
@@ -1414,6 +1414,11 @@
 		Currently supported on some MPC8xxx processors.  For an
 		example, see include/configs/mpc8349emds.h.
 
+		CONFIG_MXC_SPI
+
+		Enables the driver for the SPI controllers on i.MX and MXC
+		SoCs. Currently only i.MX31 is supported.
+
 - FPGA Support: CONFIG_FPGA
 
 		Enables FPGA subsystem.