iommu/vt-d: Fold domain_exit() into intel_iommu_domain_free()

iommu/vt-d: Fold domain_exit() into intel_iommu_domain_free()

It has only one caller, no need for two functions.

Correct the WARN_ON() error handling to leak the entire page table if the
HW is still referencing it so we don't UAF during WARN_ON recovery.

Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Signed-off-by: Jason Gunthorpe <jgg@nvidia.com>
Link: https://lore.kernel.org/r/2-v3-dbbe6f7e7ae3+124ffe-vtd_prep_jgg@nvidia.com
Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Link: https://lore.kernel.org/r/20250714045028.958850-5-baolu.lu@linux.intel.com
Signed-off-by: Will Deacon <will@kernel.org>