drm/amdgpu: increase max instance number for hw ip

max instance number is 6 for navi10 and 7 for navi14, and we increase the
reg_offset array size to avoid out-of-bound access

Signed-off-by: Xiaojie Yuan <xiaojie.yuan@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>