arm64: Force use of common clk at architecture level

Force all platforms to use the common clk framework to ensure that we do
not end up with platform-specific implementations ala ARM32.

Signed-off-by: Deepak Saxena <dsaxena@linaro.org>
Acked-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>