linux-imx

clk: make CONFIG_COMMON_CLK invisible

All platforms that use the common clk infrastructure should select
COMMON_CLK from platform code, and on all other platforms, it must
not be enabled, so there is no point making the option visible to
users, and when it is visible, we break randconfig builds.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>