tcg-arm: Move load of tlb addend into tcg_out_tlb_read

This allows us to make more intelligent decisions about the relative
offsets of the tlb comparator and the addend, avoiding any need of
writeback addressing.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-arm: Return register containing tlb addend

Preparatory to rescheduling the tlb load, and changing said register.
Continues to use R1 for now.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-arm: Remove restriction on qemu_ld output register

The main intent of the patch is to allow the tlb addend register
to be changed, without tying that change to the constraint.  But
the most common side-effect seems to be to enable usage of ldrd
with the r0,r1 pair.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-arm: Move the tlb addend load earlier

There are free scheduling slots between the sequence of
comparison instructions.  This requires changing the
register in use to avoid conflict with those compares.

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