uboot-imx

MLK-22409 imx8qm_mek: Remove the spl defconfig

imx8qm_mek_spl_defconfig was wrongly added when porting android support
from 2018.03. Since we have enabled SPL building in imx8qm_mek_defconfig,
no need to keep this defconfig

Signed-off-by: Ye Li <ye.li@nxp.com>