ARM: dts: exynos: Add and enable 32 kHz modem clock in Galaxy I9100

The PMIC has a 32768 Hz clock used by the modem which is implemented by
driver as a regulator.  Add and enable it to be sure modem get's its
signal.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Link: https://lore.kernel.org/r/20200830135200.24304-8-krzk@kernel.org