target/arm: Correct STRD atomicity

target/arm: Correct STRD atomicity

Our STRD implementation doesn't correctly implement the requirement:
 * if the address is 8-aligned the access must be a 64-bit
   single-copy atomic access, not two 32-bit accesses

Rewrite the handling of STRD to use a single tcg_gen_qemu_st_i64()
of a value produced by concatenating the two 32 bit source registers.
This allows us to get the atomicity right.

As with the LDRD change, now that we don't update 'addr' in the
course of performing the store we need to adjust the offset
we pass to op_addr_ri_post() and op_addr_rr_post().

Cc: qemu-stable@nongnu.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-id: 20250227142746.1698904-3-peter.maydell@linaro.org
(cherry picked from commit ee786ca115045a2b7e86ac3073b0761cb99e0d49)
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>