iommu/amd: Improve page fault error reporting

iommu/amd: Improve page fault error reporting

If IOMMU domain for device group is not setup properly then we may hit
IOMMU page fault. Current page fault handler assumes that domain is
always setup and it will hit NULL pointer derefence (see below sample log).

Lets check whether domain is setup or not and log appropriate message.

Sample log:
----------
 amdgpu 0000:00:01.0: amdgpu: SE 1, SH per SE 1, CU per SH 8, active_cu_number 6
 BUG: kernel NULL pointer dereference, address: 0000000000000058
 #PF: supervisor read access in kernel mode
 #PF: error_code(0x0000) - not-present page
 PGD 0 P4D 0
 Oops: 0000 [#1] PREEMPT SMP NOPTI
 CPU: 2 PID: 56 Comm: irq/24-AMD-Vi Not tainted 6.2.0-rc2+ #89
 Hardware name: xxx
 RIP: 0010:report_iommu_fault+0x11/0x90
 [...]
 Call Trace:
  <TASK>
  amd_iommu_int_thread+0x60c/0x760
  ? __pfx_irq_thread_fn+0x10/0x10
  irq_thread_fn+0x1f/0x60
  irq_thread+0xea/0x1a0
  ? preempt_count_add+0x6a/0xa0
  ? __pfx_irq_thread_dtor+0x10/0x10
  ? __pfx_irq_thread+0x10/0x10
  kthread+0xe9/0x110
  ? __pfx_kthread+0x10/0x10
  ret_from_fork+0x2c/0x50
  </TASK>

Reported-by: Matt Fagnani <matt.fagnani@bell.net>
Suggested-by: Joerg Roedel <joro@8bytes.org>
Signed-off-by: Vasant Hegde <vasant.hegde@amd.com>
Link: https://bugzilla.kernel.org/show_bug.cgi?id=216865
Link: https://lore.kernel.org/lkml/15d0f9ff-2a56-b3e9-5b45-e6b23300ae3b@leemhuis.info/
Link: https://lore.kernel.org/r/20230215052642.6016-3-vasant.hegde@amd.com
Cc: stable@vger.kernel.org
[joro: Edit commit message]
Signed-off-by: Joerg Roedel <jroedel@suse.de>