drivers: clk: Update license for Intel N5X device

All the source code of clk-mem-n5x.c and clk-n5x.c are from Intel,
update the license to use both GPL2.0 and BSD-3 Clause because this
copy of code may used for open source and internal project.

Signed-off-by: Teik Heng Chong <teik.heng.chong@intel.com>
Reviewed-by: Tien Fong Chee <tien.fong.chee@intel.com>