ARM: SAMSUNG: Introduce Kconfig variable for Samsung custom clk API

Make it easier to switch to the common clock API by making the existing
clock API implementation depend on a Kconfig symbol which is enabled when
the common clock API is disabled. This means that we can have some SoCs
using the common clock API and some using the existing API rather than
needing a flag day to convert the entire family of devices over.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>