imx6: sabrelite: update defconfig to use distro defaults

Boot tested with boot.scr script and EFI/Grub2 on mmc0 and mmc1 slots on sabrelite board.

Signed-off-by: Guillaume GARDET <guillaume.gardet@free.fr>
Cc: Troy Kisky <troy.kisky@boundarydevices.com>
Cc: Stefano Babic <sbabic@denx.de>
Cc: Fabio Estevam <fabio.estevam@nxp.com>
Cc: Gary Bisson <gary.bisson@boundarydevices.com>