drm/amdgpu: remove unnecessary variables

This fixes the warnings below, and also drops the display_count
variable, as it's unused.

 In function 'svm_range_map_to_gpu':
 warning: variable 'bo_va' set but not used [-Wunused-but-set-variable]
 1172 |         struct amdgpu_bo_va bo_va;
      |                             ^~~~~
 ...
 In function 'dcn201_update_clocks':
 warning: variable 'enter_display_off' set but not used [-Wunused-but-set-variable]
 132 |         bool enter_display_off = false;
     |              ^~~~~~~~~~~~~~~~~

Changes since v1:
- As suggested by Rodrigo Siqueira:
  1. Drop display_count variable.
- As suggested by Felix Kuehling:
  1. Remove block surrounding amdgpu_xgmi_same_hive.

Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Isabella Basso <isabbasso@riseup.net>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>