Staging: brcm80211: disable drivers for PPC platforms

Right now, bad things happen if you try to build these drivers for the
PPC platform as it seems that the code only has been tested and built on
the MIPS big endian platform.

So disable it on the PPC32 and PPC64 platforms for now, hopefully this
will be resolved in the future as I'm sure someone will want to use
these chips with that platform someday.

Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Cc: Henry Ptasinski <henryp@broadcom.com>
Cc: Brett Rudley <brudley@broadcom.com>
Cc: Roland Vossen <rvossen@broadcom.com>

Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>