drm/amdgpu: add debugfs for spirom IFWI dump

drm/amdgpu: add debugfs for spirom IFWI dump

Expose the debugfs file node for user space to dump the IFWI image
on spirom.

For one transaction between PSP and host, it will read out the
images on both active and inactive partitions so a buffer with two
times the size of maximum IFWI image (currently 16MByte) is needed.

v2: move the vbios gfl macros to the common header and rename the
    bo triplet struct to spirom_bo for this specific usage (Hawking)

v3: return directly the result of last command execution (Lijo)

Signed-off-by: Shiwu Zhang <shiwu.zhang@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Reviewed-by: Lijo Lazar <lijo.lazar@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>