Upstream uses the gpio-ranges property to define the number of GPIOs,
support for parsing this when gpio-count is unspecified

Additionally, drop the bank-name property as it isn't used in upstream,
and we can just hardcode the bank name instead.

Reviewed-by: Sumit Garg <sumit.garg@linaro.org>
Tested-by: Sumit Garg <sumit.garg@linaro.org>
Reviewed-by: Simon Glass <sjg@chromium.org>
Signed-off-by: Caleb Connolly <caleb.connolly@linaro.org>