target-mips: fix calculation of overflow for SHLL.PH and SHLL.QB

This change corrects and simplifies how discard is calculated for shift
left logical vector instructions. It is used to detect overflow and set bit
22 in the DSPControl register.

The existing tests (shll_ph.c, shll_qb.c) are extended with the corner cases
that expose incorrectness in the previous implementation.

Signed-off-by: Petar Jovanovic <petar.jovanovic@imgtec.com>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
tcg-arm: Fix 64-bit tlb load for pre-v6

Found by inspection, since the effect of the bug was simply to
send all memory ops through the slow path.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
tcg-arm: Use movi32 in exit_tb

Avoid the mini constant pool for armv7, and avoid replicating
the test for pre-v7.

Signed-off-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>