drm/amdgpu: Rename flag which prevents HW access

Make it's name not feature but function descriptive.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20210521204122.762288-1-andrey.grodzovsky@amd.com