tcg-ppc: Fix and cleanup tcg_out_tlb_check

The fix is that sparc has so many mmu modes that the last one overflowed
the 16-bit signed offset we assumed would fit.  Handle this, and check
the new assumption at compile time.

Load the tlb addend earlier for the fast path.

Remove the explicit address + addend and make use of index addressing.

Adjust constraints for qemu_ld64 such that we don't clobber the address
register or tlb addend before loading both values.

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