clk: keystone: add missing MODULE_LICENSE

A randconfig build showed that two clk modules have no license tag:

WARNING: modpost: missing MODULE_LICENSE() in drivers/clk/keystone/gate.o
see include/linux/module.h for more information
WARNING: modpost: missing MODULE_LICENSE() in drivers/clk/keystone/pll.o
see include/linux/module.h for more information

Add the appropriate information from the comment at the start of the
two files.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Acked-by: Santosh Shilimkar <ssantosh@krenel.org>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>