x86: Use the generic bitops headers

Use the generic bitops and also add custom __ffs() implementation
as per the kernel.

Also align the ffs() implementation with the kernel.

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>