tcg-mips: Convert to new qemu_l/st helpers

In addition, fill delay slots calling the helpers and tail
call to the store helpers.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-mips: Tidy tcg_out_call_iarg routines

Hoist pointer argument load.  Store from zero when appropriate.

Signed-off-by: Richard Henderson <rth@twiddle.net>
tcg-mips: Convert to new_ldst

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