drm/amdgpu/psp: Get psp fw version through reading register

If PSP FW is running already, driver will not load PSP FW again and skip
it. So psp fw version is not correct if reading it from FW binary file,
need to get right version from register.

Signed-off-by: Xiangliang Yu <Xiangliang.Yu@amd.com>
Acked-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>