drm/amd/pp: Connect display_clock_voltage_request to a function pointer

Get rid of an empty dublicate of smu10_display_clock_voltage_request

Add display_clock_voltage_request to smu10 functions struct so it
can be called from outside the class and connect the pointer to
the function.

That way Display driver can finally apply clock voltage requests
when needed.

Signed-off-by: Mikita Lipski <mikita.lipski@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>