tcg/ia64: fix and optimize ld/st slow path

tcg/ia64: fix and optimize ld/st slow path

Store slow path has been broken in e141ab52d:
- the arguments are shifted before the last one (mem_index) is written.
- the shift is done for both slow and fast paths.

Fix that. Also optimize a bit by bundling the move together. This still
can be optimized, but it's better to wait for a decision to be taken on
the arguments order.

Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
(cherry picked from commit d03c98d80ffb7c561d9e6874580f52fe7ecc8c6c)

Signed-off-by: Michael Roth <mdroth@linux.vnet.ibm.com>