spi_mpc83xx: add OF platform driver bindings

Implement full support for OF SPI bindings.  Now the driver can manage its
own chip selects without any help from the board files and/or fsl_soc
constructors.

The "legacy" code is well isolated and could be removed as time goes by.
Signed-off-by: Anton Vorontsov <avorontsov@ru.mvista.com>
Cc: David Brownell <david-b@pacbell.net>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Kumar Gala <galak@gate.crashing.org>
Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

include/linux/fsl_devices.h

@@ -99,7 +99,7 @@ struct spi_device;
 
 struct fsl_spi_platform_data {
 	u32 	initial_spmode;	/* initial SPMODE value */
-	u16	bus_num;
+	s16	bus_num;
 	bool	qe_mode;
 	/* board specific information */
 	u16	max_chipselect;