sf: dataflash: add support for "extended ID"

Take as reference Linux kernel code:
	drivers/mtd/devices/mtd_dataflash.c
	commit 1da8869a428317a6d3cd8d47184cf87feb34a98b
	Author: Andrey Smirnov <andrew.smirnov@gmail.com>

Signed-off-by: Luca Ellero <luca.ellero@brickedbrain.com>
Reviewed-by: Jagan Teki <jagan@amarulasolutions.com>