firmware_loader: move struct builtin_fw to the only place used

Now that x86 doesn't abuse picking at internals to the firmware
loader move out the built-in firmware struct to its only user.

Reviewed-by: Borislav Petkov <bp@suse.de>
Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Link: https://lore.kernel.org/r/20211021155843.1969401-5-mcgrof@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>