clk: keystone: Build Keystone clock drivers

Now build the keystone common clock drivers. The build is made
conditional based on COMMON_CLK_KEYSTONE

Signed-off-by: Santosh Shilimkar <santosh.shilimkar@ti.com>
Signed-off-by: Mike Turquette <mturquette@linaro.org>

diff --cc drivers/clk/Kconfig
Simple merge

diff --cc drivers/clk/Makefile
Simple merge

diff --cc drivers/clk/keystone/Makefile
Simple merge