pinctrl: intel: Add ~4k bias support

All versions that have 20k and 5k resistance, i.e. all that
the driver supports, may support ~4k when the above mentioned
are connected in parallel. Add such a support.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>