mtd: brcmnand: iProc big endian and ONFI support

This patch adds big endian and ONFI support for various iProc based
SoCs that use the core brcmstb NAND controller

This patch was originally implemented by Prafulla Kota
<prafulla.kota@broadcom.com> and fully tested on iProc based NS2 SVK

Signed-off-by: Prafulla Kota <prafulla.kota@broadcom.com>
Signed-off-by: Ray Jui <ray.jui@broadcom.com>
Reviewed-by: Kamal Dasu <kdasu.kdev@gmail.com>
Acked-by: Kamal Dasu <kdasu.kdev@gmail.com>
Signed-off-by: Boris Brezillon <boris.brezillon@free-electrons.com>