drm/amdgpu/mes: fetch fw version from firmware header

We need this prior to the firmware being loaded so fetch
from the header.

v2: fetch directly from the firmware
v3: store both fw versions

Reviewed-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>