drm/amd/pm: Remove remainder of mode2_reset_is_support

The previous patch removed smu_mode2_reset_is_support()
which was the only function to call through the mode2_reset_is_support()
method pointer.

Remove the remaining functions that were assigned to it
and the pointer itself.

See discussion at:
https://lore.kernel.org/all/DM4PR12MB5165D85BD85BC8FC8BF7A3B48E88A@DM4PR12MB5165.namprd12.prod.outlook.com/



Signed-off-by: Dr. David Alan Gilbert <linux@treblig.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>