drm/imx: imx-tve: depend on COMMON_CLK

Since the TVE provides a clock to the DI, the driver can only be
compiled if the common clock framework is enabled. With the COMMON_CLK
dependency in place, it will be possible to allow building the other
parts of imx-drm under COMPILE_TEST on architectures that do not select
the common clock framework.

Signed-off-by: Philipp Zabel <p.zabel@pengutronix.de>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>