This adds Linux booting to the SPL

This depends on CONFIG_MACH_TYPE patch by Igor Grinberg
(http://article.gmane.org/gmane.comp.boot-loaders.u-boot/105809)

Related CONFIGs:
CONFIG_SPL_OS_BOOT
	Activates/Deactivates the OS booting feature
CONFIG_SPL_OS_BOOT_KEY
	defines the IO-pin number u-boot switch - if pressed u-boot is
	booted
CONFIG_SYS_NAND_SPL_KERNEL_OFFS
	Offset in NAND of direct boot kernel image to use in SPL
CONFIG_SYS_SPL_ARGS_ADDR
	Address where the kernel boot arguments are expected - this is
	normaly RAM-begin + 0x100
Signed-off-by: NSimon Schwarz <simonschwarzcor@gmail.com>
CC: Tom Rini <tom.rini@gmail.com>
CC: Stefano Babic <sbabic@denx.de>
CC: Wolfgang Denk <wd@denx.de>