target-alpha: Fix translation of PALmode memory insns.

All of the "raw" memory accesses should be "phys" instead.  Fix
some confusion about argument ordering of the store routines.
Fix the implementation of store-conditional.

Delete the "alt-mode" helpers.  Because we only implement two
mmu modes, let /a imply user-mode unconditionally.

Leave some combinations of virt access without permission
checks as unimplemented.  There are too many hoops through
which to jump, and these insns will not be needed in the
emulation palcode.

Signed-off-by: Richard Henderson <rth@twiddle.net>
