clk: Add support to set custom flags with clk_set_flags

The new API clk_set_flags could be used by hardware specific clock drivers
or clients for specific hardware requirements. These flags could be custom
defined as per hardware needs.

Change-Id: Ia67373ee2b8934c898052c68338fa86cb16070dd
Signed-off-by: Taniya Das <tdas@codeaurora.org>
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>