Revert "powerpc/64s: Add support for a store forwarding barrier at kernel entry/exit"

Revert "powerpc/64s: Add support for a store forwarding barrier at kernel entry/exit"

BugLink: http://bugs.launchpad.net/bugs/1773162
IBM believes the backport of this patch was done incorrectly.  Revert
this commit, and a new version of the commit is being set in this patch
set.

This reverts commit 06f7e3d39f2fa4f648d94a51d809b10f98399f91.

Signed-off-by: Joseph Salisbury <joseph.salisbury@canonical.com>
Acked-by: Stefan Bader <stefan.bader@canonical.com>
Acked-by: Kleber Souza <kleber.souza@canonical.com>
Signed-off-by: Khalid Elmously <khalid.elmously@canonical.com>