powerpc/8xx: Revert commit e0908085

The commit e0908085 ("powerpc/8xx: Fix
regression introduced by cache coherency rewrite") is not needed
anymore.  The issue was because dcbst wrongly sets the store bit when
causing a DTLB error, but this is now fixed by commit
0a2ab51f ("powerpc/8xx: Fixup DAR from
buggy dcbX instructions.") which handles the buggy dcbx instructions on
data page faults on the 8xx.

Signed-off-by: Christophe Leroy <christophe.leroy@c-s.fr>
[scottwood@freescale.com: fix commit message]
Signed-off-by: Scott Wood <scottwood@freescale.com>