iommu/amd: Add debugfs support to dump device table

IOMMU uses device table data structure to get per-device information for
DMA remapping, interrupt remapping, and other functionalities. It's a
valuable data structure to visualize for debugging issues related to
IOMMU.

eg.
-> To dump device table entry for a particular device
   #echo 0000:c4:00.0 > /sys/kernel/debug/iommu/amd/devid
   #cat /sys/kernel/debug/iommu/amd/devtbl

   or

   #echo c4:00.0 > /sys/kernel/debug/iommu/amd/devid
   #cat /sys/kernel/debug/iommu/amd/devtbl

Signed-off-by: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Link: https://lore.kernel.org/r/20250702093804.849-7-dheerajkumar.srivastava@amd.com


Signed-off-by: Will Deacon <will@kernel.org>