iommu/vt-d: Remove comment for def_domain_type

The comment for def_domain_type is outdated. Part of it is irrelevant.
Furthermore, it could just be deleted since the iommu_ops::def_domain_type
callback is properly documented in iommu.h, so individual implementations
shouldn't need to repeat that. Remove it to avoid confusion.

Signed-off-by: Lu Baolu <baolu.lu@linux.intel.com>
Reviewed-by: Kevin Tian <kevin.tian@intel.com>
Link: https://lore.kernel.org/r/20240624024327.234979-1-baolu.lu@linux.intel.com
Link: https://lore.kernel.org/r/20240702130839.108139-3-baolu.lu@linux.intel.com
Signed-off-by: Will Deacon <will@kernel.org>

Author: LuBaolu

drivers/iommu/intel/iommu.c

@@ -2177,17 +2177,6 @@ static bool device_rmrr_is_relaxable(struct device *dev)
 		return false;
 }
 
-/*
- * Return the required default domain type for a specific device.
- *
- * @dev: the device in query
- * @startup: true if this is during early boot
- *
- * Returns:
- *  - IOMMU_DOMAIN_DMA: device requires a dynamic mapping domain
- *  - IOMMU_DOMAIN_IDENTITY: device requires an identical mapping domain
- *  - 0: both identity and dynamic domains work for this device
- */
 static int device_def_domain_type(struct device *dev)
 {
 	if (dev_is_pci(dev)) {