drm/amdgpu/gfx10: fix KGQ reset sequence

Need to reinit the ring before remapping it and all of
the KIQ handling needs to be within the kiq lock.

Fixes: 1741281a ("drm/amdgpu/gfx10: add ring reset callbacks")
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>