drm/amd/display: Check validation passed after applying pipe split changes

[WHY?]
Validation can fail for configurations that were previously supported, by only
changing parameters such as the DET allocations, which is currently unexpected.

[HOW?]
Add a check that validation passes after applying pipe split related changes.

Reviewed-by: Alvin Lee <Alvin.Lee2@amd.com>
Acked-by: Alex Hung <alex.hung@amd.com>
Signed-off-by: Dillon Varone <Dillon.Varone@amd.com>
Tested-by: Mark Broadworth <mark.broadworth@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>