Add a check for CONFIG_SKIP_RELOCATE in reserve_uboot to skip the
relocation of the U-Boot image.
CONFIG_SKIP_RELOCATE skips relocation of U-Boot to the end of RAM
allowing for systems that have extremely limited RAM to run U-Boot.

Signed-off-by: Jesse Taube <Mr.Bossman075@gmail.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Caleb Connolly <caleb.connolly@linaro.org>
Reviewed-by: Fabio Estevam <festevam@gmail.com>