dt-bindings: qcom,pmic-gpio: Add pm2250 compatible string

Add compatible strings for pm2250 SPMI GPIO to documentation.

Signed-off-by: Loic Poulain <loic.poulain@linaro.org>
Link: https://lore.kernel.org/r/1637076915-3280-2-git-send-email-loic.poulain@linaro.org


Signed-off-by: Linus Walleij <linus.walleij@linaro.org>