drm/amdgpu: Save some cycles on the job submission path

Every job submission on the Steam Deck ends up walking the list of IP
blocks looking for AMD_IP_BLOCK_TYPE_SMC. Half of the call chain is like
the below, while the second half is from amdgpu_gfx_profile_ring_end_use:

 amdgpu_gfx_profile_ring_begin_use
  amdgpu_dpm_is_overdrive_enabled
   is_support_sw_smu
    amdgpu_device_ip_is_valid

On a game menu screen at 90Hz refresh rate we end up with ~840 calls per
second which sticks out when the submission worker is profiled with perf:

  13.78%  [kernel]  [k] __lock_text_start
  10.86%  [kernel]  [k] __lookup_object
   8.76%  [kernel]  [k] __mod_timer
   4.94%  [kernel]  [k] queued_spin_lock_slowpath
   1.66%  [kernel]  [k] amdgpu_device_ip_is_valid
   1.54%  [kernel]  [k] preempt_count_add
   1.42%  [kernel]  [k] amdgpu_sync_peek_fence
   1.18%  [kernel]  [k] amdgpu_vmid_grab
   1.17%  [kernel]  [k] amdgpu_ib_schedule
   1.14%  [kernel]  [k] kthread_worker_fn

Lets short-circuit this walk by simply caching the result of
is_support_sw_smu() in the device.

This is a micro-improvement but it is at least conceptually nicer to avoid
repeating the same walk so much.

Reviewed-by: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@igalia.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: Christian König <christian.koenig@amd.com>
Cc: Timur Kristóf <timur.kristof@gmail.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

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