drm/amdgpu: correct programming of ih_chicken for Arcturus

ih_chicken is a register that is not allowed to access by driver
in the L0 security policy.
psp bl need to enable field to allow driver to use physical
bus address for ih ring on secure part.

Signed-off-by: Le Ma <le.ma@amd.com>
Reviewed-by: Snow Zhang <snow.zhang@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>