dt-bindings: pinctrl: mediatek,mt6779-pinctrl: Improve description

dt-bindings: pinctrl: mediatek,mt6779-pinctrl: Improve description

The current description mentions having to put the pin controller
node under a syscon node, but this is not the case in the current
MT6779 device tree. This is not actually needed, so replace the
current description with something more generic that describes
the use of the hardware block.

Signed-off-by: Yassine Oudjana <y.oudjana@protonmail.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
Link: https://lore.kernel.org/r/20221028153505.23741-3-y.oudjana@protonmail.com
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>