Blackfin: push access_ok() L1 attribute down

There is no need for the L1 attribute to be on the prototype of the
access_ok() function as all consumers of the function do not care where it
lives -- they'll always use pcrel calls to get to it.  This prevents
pointless recompiles of most of the system when this config option changes.

Signed-off-by: Mike Frysinger <vapier@gentoo.org>