Just by running `make kernel_oldconfig` and unsetting following options
manually as those cores are cortex-a7 based and thus irrelevant for the
currently default cortex-a9 used cores.
CONFIG_CLK_IMX6SL is not set
CONFIG_CLK_IMX6SX is not set
CONFIG_CLK_IMX6UL is not set
Signed-off-by: Petr Štetiar <ynezz@true.cz>