This is a port of the read data bus interface from the Linux
brcmnand driver, commit 546e425991205f59281e160a0d0daed47b7ca9b3
"mtd: rawnand: brcmnand: Add BCMBCA read data bus interface"

This is needed for the BCMBCA RAW NAND driver.

Signed-off-by: William Zhang <william.zhang@broadcom.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: William Zhang <william.zhang@broadcom.com>