iommu/amd: Refactor AMD IOMMU debugfs initial setup

Rearrange initial setup of AMD IOMMU debugfs to segregate per IOMMU
setup and setup which is common for all IOMMUs. This ensures that common
debugfs paths (introduced in subsequent patches) are created only once
instead of being created for each IOMMU.

With the change, there is no need to use lock as amd_iommu_debugfs_setup()
will be called only once during AMD IOMMU initialization. So remove lock
acquisition in amd_iommu_debugfs_setup().

Signed-off-by: Dheeraj Kumar Srivastava <dheerajkumar.srivastava@amd.com>
Reviewed-by: Suravee Suthikulpanit <suravee.suthikulpanit@amd.com>
Reviewed-by: Vasant Hegde <vasant.hegde@amd.com>
Link: https://lore.kernel.org/r/20250702093804.849-2-dheerajkumar.srivastava@amd.com


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