When emulating an unaligned load/store, load the instruction via $epcc rather
than straight, as when in a sandbox the instruction isn't at an untransformed
$pc.  Add some comments to the effect that this isn't quite sufficient -- we
need to handle the fact that this 'clw' (and other simmilar ones) might throw
an exception if $epcc wasn't valid for the access, which they currently don't.
On a related note, they also require CHERI_PERM_LOAD, which isn't currently
set, but will be in the next commit.  Clearly more to sort out here.
Set CHERI_PERM_LOAD on code capabilities, as the kernel will expect this so
that it can load instructions via $epcc + $pc when performing emulations.
It's not clear this is really the right/best solution, but it is useful in
the mean time.