In powerpc table, fix macros los() and his().

In powerpc table, fix macros los() and his().

Change the operator in his() from a - minus to a + plus.  When los(n)
becomes negative, then his(n) needs to add 0x10000, not subtract it.

Also change los(n) to do the sign extension, because smalls(los(n))
should be true, not false.

Also change hi(n) and lo(n) to wrap n in parentheses, as (n), because
these are macros and n might still contain operators.