drm/amdkfd: replace kgd_dev in static gfx v7 funcs

Static funcs in amdgpu_amdkfd_gfx_v7.c now using amdgpu_device.

Signed-off-by: Graham Sider <Graham.Sider@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>