[PowerPC] Use zext instead of anyext in custom and combine (#68784)

This custom combine currently converts `and(anyext(x),c)` into
`anyext(and(x,c))`. This is not correct, because the original expression
guaranteed that the high bits are zero, while the new one sets them to
undef.

Emit `zext(and(x,c))` instead.

Fixes https://github.com/llvm/llvm-project/issues/68783.