We introduced a variable called mmu_on to the mmu implementation
because unit tests may want to run with the mmu off, yet still
call into common code that could lead to {Load,Store}-Exclusive
instructions - which is illegal. So, the mmu_on variable was added
and made query-able (through mmu_enabled()) in order to guard those
paths. But, mmu_on is really a per cpu concept, so for smp we need
to change it. As it's just a bool, we can easily make it per cpu by
changing it into a cpumask. We rename it more appropriately too.

Signed-off-by: Andrew Jones <drjones@redhat.com>
Signed-off-by: Marcelo Tosatti <mtosatti@redhat.com>