tcg/mips: Reorg tlb load within prepare_host_addr

tcg/mips: Reorg tlb load within prepare_host_addr

Compare the address vs the tlb entry with sign-extended values.
This simplifies the page+alignment mask constant, and the
generation of the last byte address for the misaligned test.

Move the tlb addend load up, and the zero-extension down.

This frees up a register, which allows us use TMP3 as the returned base
address register instead of A0, which we were using as a 5th temporary.

Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>