sf: Set quad enable bit support

This patch provides support to set the quad enable bit on flash.

quad enable bit needs to set before performing any quad IO
operations on respective SPI flashes.

Currently added set  quad enable bit for winbond and spansion flash
devices. stmicro flash doesn't require to set as qeb is volatile.
remaining flash devices support will add in future patches.

Signed-off-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>