drm/amdgpu/psp12: move ih_reroute into ring_create

This matches what we do for psp 3.1 and makes ring_init
common for all PSP versions.

Acked-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>