As mx6sabreauto supports SPL now, all variants can boot using the same
defconfig.
This patch:
- Removes non-SPL targets.
- Renames target to mx6sabreauto_defconfig.
- Renames folder and board files to mx6sabreauto.
- Updates MAINTAINERS, Makefile and Kconfig accordingly.
- Removes .cfg files.
- Adds a README with instructions to build and flash SPL and u-boot.img.
Signed-off-by: Vanessa Maegima
Reviewed-by: Fabio Estevam
Reviewed-by: Stefano Babic
