powerpc: Remove __ilog2_u64 and ffs4 from bitops

powerpc: Remove __ilog2_u64 and ffs4 from bitops

Remove __ilog2_u64 and ffs4 from powerpc bitops to align with the
kernel implementation.

Use the generic __ffs64 instead of a custom powerpc implementation.

Cc: York Sun <[email protected]>
Signed-off-by: Fabio Estevam <[email protected]>
Reviewed-by: Tom Rini <[email protected]>
Reviewed-by: Heiko Schocher <[email protected]>
Reviewed-by: Jagan Teki <[email protected]>