gpio: rcar: select General Output Register to set output states

R-Car GPIO controller provides two interfaces to set GPIO line output
signal state, and for a particular GPIO line the selected interface is
determined by OUTDTSEL bit value.

At the moment the driver supports only one of two interfaces, namely
OUTDT General Output Register is used to control the output signal.

While this selection is the default one on reset, it is not explicitly
configured on probe, thus it might be possible that kernel and userspace
consumers of a GPIO won't be able to set the wanted GPIO output signal.

Below is a simple test case to reproduce the described problem and
verify this fix in the kernel on H3 ULCB by setting non-default OUTDTSEL
configuration from a bootloader:

  u-boot    > mw.l 0xe6055440 0x3000 1
  ...
  userspace > echo default-on > /sys/devices/platform/leds/leds/led5/trigger
  userspace > echo default-on > /sys/devices/platform/leds/leds/led6/trigger

Signed-off-by: Vladimir Zapolskiy <vladimir_zapolskiy@mentor.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>