pinctrl: tangier: Move default strength assignment to a switch-case

iWhen ->pin_config_set() is called from the GPIO library (assumed
GpioIo() ACPI resource), the argument can be 1, when, for example,
PullDefault is provided. In such case we supply sane default in
the driver. Move that default assingment to a switch-case, so
it will be consolidated in one place.

Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Reviewed-by: Raag Jadav <raag.jadav@intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>