[U-Boot] mxc_spi refactoring (for mx6q)

[Eric Nelson]

This patch set refactors mxc_spi as described in 
    http://lists.denx.de/pipermail/u-boot/2010-March/068791.html
and requested in 
    http://lists.denx.de/pipermail/u-boot/2012-January/116023.html
in order to add support for the MX6Q in general and the mx6qsabrelite 
specifically.

Patch 1 simply moves the conditional parts of mxc_spi.c into the
respective CPU-specific imx-regs.h files.

Patch 2 adds general support for SPI to the i.MX6.

Patch 3 adds support to the mx6qsabrelite board

Patch 4 modifies the 'sf' command to allow a default chip-select
to be specified by board headers as is done on efika et al. This allows
a bare 'sf' probe command:
     U-Boot> sf probe
instead of the more cumbersome usage when a GPIO is tacked onto
the chip-select. Otherwise, this command-line would be needed  
to specify GP3:19 on SabreLite:
     U-Boot> sf probe 0x5300   

Patch 5 adds default chip-select values for mx6qsabrelite platform.

Patch 6 adds reference macros for use in storing the environment
in serial flash to match the use on Freescale's U-Boot release

This patch set has been compiled against the following configurations,
but only tested on mx6qsabrelite:
	mx6qsabrelite
	mx51evk
	mx31pdk
	mx35pdk