drm/amd/pm: avoid potential UBSAN issue on legacy asics

Prevent further dpm casting on legacy asics without od_enabled in
amdgpu_dpm_is_overdrive_supported. This can avoid UBSAN complain
in init sequence.

v2: add a macro to check legacy dpm instead of checking asic family/type
v3: refine macro name for naming consistency

Suggested-by: Evan Quan <evan.quan@amd.com>
Signed-off-by: Guchun Chen <guchun.chen@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org