drm/amdgpu: unify BO evicting method in amdgpu_ttm

drm/amdgpu: unify BO evicting method in amdgpu_ttm

BugLink: https://bugs.launchpad.net/bugs/1972134
Unify BO evicting functionality for possible memory
types in amdgpu_ttm.c.

Signed-off-by: Nirmoy Das <nirmoy.das@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
(cherry picked from commit 58144d283712c9e80e528e001af6ac5aeee71af2)
Signed-off-by: Kai-Heng Feng <kai.heng.feng@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Tim Gardner <tim.gardner@canonical.com>
Signed-off-by: Stefan Bader <stefan.bader@canonical.com>