alpha: kill big kernel lock

All uses of the BKL on alpha are totally bogus, nothing
is really protected by this. Remove the remaining users
so we don't have to mark alpha as 'depends on BKL'.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Cc: Richard Henderson <rth@twiddle.net>
Cc: Ivan Kokshaysky <ink@jurassic.park.msu.ru>
Cc: Matt Turner <mattst88@gmail.com>
Cc: linux-alpha@vger.kernel.org