drm/amdgpu: Switch to VRAM buffer for USBC PD FW.

System memory-based implementation for updating the
USBCPD is deprecated for so switching
to LFB based implementation for all the ASICs.

Signed-off-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Reviewed-by: Alexander Deucher <Alexander.Deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>