The DCBZL instruction is not available for the e500v1 and e500v2
architectures, but may still be recognized by the toolchain, so we
need to explicitly disable it for these architectures.

References: PowerPC™ e500 Core Family Reference Manual (Freescale)
Found-by: Ståle Kristoffersen <staalebk@ifi.uio.no>
Signed-off-by: Vittorio Giovara <vittorio.giovara@gmail.com>