pinctrl: Add pinctrl binding for Broadcom Capri SoCs

Adds pinctrl driver devicetree binding for Broadcom Capri (BCM281xx) SoCs.

v4: Changed valid values for "bias-pull-up" property for I2C pins.
    Expanded pin configuration node example.
v3: Use generic pin config properties instead of brcm-specific ones.
    Clarified pin types (standard, i2c, hdmi).
v2: Use hyphens instead of underscore in DT property names.

Device tree bindings maintainers ECG:
           _             _          _        _        _
__________/ \   ________/ \   _____/ \   ___/ \   ___/ \   __
             \_/           \_/        \_/      \_/      \_/

Signed-off-by: Sherman Yin <syin@broadcom.com>
Reviewed-by: Christian Daudt <bcm@fixthebug.org>
Reviewed-by: Matt Porter <matt.porter@linaro.org>
Acked-by: Mark Rutland <mark.rutland@arm.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>