drm/amdgpu: Add support for USBC PD FW download

Starts USBC PD FW download and reads back the latest FW version.

v2:
Move sysfs file creation to late init
Add locking around PSP calls to avoid concurrent access to PSP's C2P registers

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