[U-Boot] mxc_spi refactoring (for mx6q)

[Marek Vasut <marek.vasut@gmail.com>]

> 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

Muhehehe ... time for a little review-torture :-)