drm/amdgpu: increase size of psp fw_name string(v2)

Increase fw_name string size so longer chip name can be stored.

v2: define macro for the length of psp fw name.

Signed-off-by: Tao Zhou <tao.zhou1@amd.com>
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>