target/arm: Bring VLSTM/VLLDM helper store/load closer to the ARM pseudocode

target/arm: Bring VLSTM/VLLDM helper store/load closer to the ARM pseudocode

This patch brings the VLSTM and VLLDM helper functions closer to the ARM
pseudocode by adding MO_ALIGN to the MemOpIdx of the associated store
(`cpu_stl_mmu`) operations and load (`cpu_ldl_mmu`) operations.

Note that this is not a bug fix: an 8-byte alignment check already exists
and remains in place, enforcing stricter alignment than the 4 bytes
requirement in the individual loads and stores. This change merely makes the
helper implementations closer to the ARM pseudocode.

That said, as a side effect, the MMU index is now resolved once instead of
on every `cpu_*_data_ra` call, reducing redundant lookups

Signed-off-by: William Kosasih <kosasihwilliam4@gmail.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250703085604.154449-2-kosasihwilliam4@gmail.com
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>