Blackfin: fix MPU handling of invalid memory accesses

The protect_page() function was incorrectly setting up the hardware tables
based on possible access capabilities rather than the actual requested
values.  This means we would grant more access to mmap-ed pages than we
should have.  Once we fix this, we need to tweak the signal generated by
such accesses to aline ourselves with other ports.  This allows the LTP
mmap0{5,6,7} cases to run properly.

Signed-off-by: Graf Yang <graf.yang@analog.com>
Signed-off-by: Mike Frysinger <vapier@gentoo.org>