Avoid a loop in the tlb_fill path; the fill will either succeed or
generate an exception.

Inline the slow_ld/st function; it was a complete copy of the main
helper except for the actual cross-page unaligned code, and the
compiler was inlining it anyway.

Add unlikely markers optimizing for the most common case of simple
tlb miss.

Make sure the compiler can optimize away the unaligned paths for a
1 byte access.
Reviewed-by: NAurelien Jarno <aurelien@aurel32.net>
Signed-off-by: NRichard Henderson <rth@twiddle.net>