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 <yorksun@freescale.com>
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Jagan Teki <jteki@openedev.com>