drm/amd/display: Use switch table for dc_to_smu_clock_type

Using a static int array will cause errors if the given dm_pp_clk_type
is out-of-bounds. For robustness, use a switch table, with a default
case to handle all invalid values.

v2: 0 is a valid clock type for smu_clk_type. Return SMU_CLK_COUNT
    instead on invalid mapping.

Signed-off-by: Leo Li <sunpeng.li@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>