drm/amd/display: Fallback to clocks which meet requested voltage on DCN31

[WHY]
On certain configs, SMU clock table voltages don't match which cause parser
to behave incorrectly by leaving dcfclk and socclk table entries unpopulated.

[HOW]
Currently the function that finds the corresponding clock for a given voltage
only checks for exact voltage level matches. In the case that no match gets
found, parser now falls back to searching for the max clock which meets the
requested voltage (i.e. its corresponding voltage is below requested).

Signed-off-by: Michael Strauss <michael.strauss@amd.com>
Reviewed-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>