drm/amd/display: Block SubVP on displays that have pixclk > 1800Mhz

drm/amd/display: Block SubVP on displays that have pixclk > 1800Mhz

[Description]
- Enabling SubVP on high refresh rate displays had a side effect
  of also enabling on high bandwidth displays such as 8K60
- However, these are not validated and should be blocked for
  the time being
- Block SubVP on displays that have pix rate > 1800Mhz (includes
  8K60 displays)

Reviewed-by: Jun Lei <Jun.Lei@amd.com>
Reviewed-by: Nevenko Stupar <Nevenko.Stupar@amd.com>
Cc: Mario Limonciello <mario.limonciello@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Alvin Lee <Alvin.Lee2@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>