drm/amdgpu: add drv_vram_usage_va for virt data exchange

For vram_usagebyfirmware_v2_2, fw_vram_reserve is not used. So
fw_vram_usage_va is NULL, and cannot do virt data exchange
anymore. Should add drv_vram_usage_va to do virt data exchange
in vram_usagebyfirmware_v2_2 case. And refine some code style
checks in pre add vram reservation logic patch

Signed-off-by: Tong Liu01 <Tong.Liu01@amd.com>
Acked-by: Luben Tuikov <luben.tuikov@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>