firmware: provide stubs for the FW_LOADER=n case

libsas has a case where it uses the firmware loader to provide services,
but doesn't want to select it all the time.  This currently causes a
compile failure in libsas if FW_LOADER=n.  Fix this by providing error
stubs for the firmware loader API in the FW_LOADER=n case.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Cc: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>