drm/amdgpu: remove switch from amdgpu_gmc_noretry_set

Simplify the logic in amdgpu_gmc_noretry_set by getting rid of the
switch. Also set noretry=1 as default for GFX 10.3.0 and greater since
retry faults are not supported.

Signed-off-by: Graham Sider <Graham.Sider@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>