drm/amdkfd: Don't split unchanged SVM ranges

If an existing SVM range overlaps an svm_range_set_attr call, we would
normally split it in order to update only the overlapping part.
However, if the attributes of the existing range would not be changed
splitting it is unnecessary.

Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Philip Yang <Philip.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>