clk: qcom: clk-dummy: Add a dummy clock provider

Add a dummy clock provider that registers a simple callback that
in turn always returns the dummy clock for any clk_get call. This
is useful for unimplemented clocks.

CRs-Fixed: 1047055
Change-Id: I08fcb174fd0e0c49f8069e106b48597bcdfe847d
Signed-off-by: Taniya Das <tdas@codeaurora.org>
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>