For Sx1504/5/6 only SX1506 has RegAdvanced, so put some code in place to
account for that.
Tested-by: NNeil Armstrong <narmstrong@baylibre.com>
Acked-by: NNeil Armstrong <narmstrong@baylibre.com>
Signed-off-by: NAndrey Smirnov <andrew.smirnov@gmail.com>
Signed-off-by: NLinus Walleij <linus.walleij@linaro.org>