target/hppa: Include PSW_P in tb flags and mmu index

Use a separate mmu index for PSW_P enabled vs disabled.
This means we can elide the tlb flush in cpu_hppa_put_psw
when PSW_P changes.  This turns out to be the majority
of all tlb flushes.

Signed-off-by: Richard Henderson <richard.henderson@linaro.org>