drm/amdgpu: add cgs_get_firmware_info interface v2

This new interface can be used by IP components to retrieve the
firmware information from the core driver.

v2: fix one typo

Signed-off-by: Jammy Zhou <Jammy.Zhou@amd.com>
Signed-off-by: Rex Zhu <Rex.Zhou@amd.com>
Signed-off-by: Young Yang <Young.Yang@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>