drm/amd/powerplay: add helper of smu_clk_dpm_is_enabled for smu

v2: change function name to smu_clk_dpm_is_enabled.
add this helper function to check dpm clk feature is enabled.

Signed-off-by: Kevin Wang <kevin1.wang@amd.com>
Reviewed-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>