sf: Add bank address register writing support

This patch provides support to program a flash bank address
register.

extended/bank address register contains an information to access
the 4th byte addressing in 3-byte address mode.

reff' the spec for more details about bank addr register
in Page-63, Table 8.16
http://www.spansion.com/Support/Datasheets/S25FL128S_256S_00.pdf



Signed-off-by: Jagannadha Sutradharudu Teki <jaganna@xilinx.com>
Reviewed-by: Simon Glass <sjg@chromium.org>