drm/amdkfd: Remove svm range validated_once flag

drm/amdkfd: Remove svm range validated_once flag

[ Upstream commit c99b16128082de519975aa147d9da3e40380de67 ]

The validated_once flag is not used after the prefault was removed, The
prefault was needed to ensure validate all system memory pages at least
once before mapping or migrating the range to GPU.

Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Stable-dep-of: eb3c357bcb28 ("drm/amdkfd: Handle errors from svm validate and map")
Signed-off-by: Sasha Levin <sashal@kernel.org>