drm/amd/pm: power up or down vcn by instance

For smu ip with multiple vcn instances (smu 11/13/14), remove all the
for loop in dpm_set_vcn_enable() functions. And use the instance
argument to power up/down vcn for the given instance only, instead
of powering up/down for all vcn instances.

v2: remove all duplicated functions in v1.

remove for-loop from each ip, and temporarily move to dpm_set_vcn_enable,
in order to keep the exact same logic as before, until further separation
in the next patch.

Signed-off-by: Boyuan Zhang <boyuan.zhang@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>