dt-bindings: mfd: sprd,sc2731: Convert to YAML

dt-bindings: mfd: sprd,sc2731: Convert to YAML

Convert the Spreadtrum SC27xx PMIC bindings to DT schema. Adjust the
filename to match the compatible of the only in-tree user, SC2731.
Change #interrupt-cells value to 1, as according to [1] that is the
correct value.
Move partial examples of child nodes in the child node schemas to this new
MFD schema to have one complete example.

[1] https://lore.kernel.org/lkml/b6a32917d1e231277d240a4084bebb6ad91247e3.1550060544.git.baolin.wang@linaro.org/

Signed-off-by: Stanislav Jakubek <stano.jakubek@gmail.com>
Reviewed-by: Rob Herring (Arm) <robh@kernel.org>
Acked-by: Sebastian Reichel <sre@kernel.org>
Acked-by: Alexandre Belloni <alexandre.belloni@bootlin.com>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Link: https://lore.kernel.org/r/efd200c3b5b75405e4e450d064b026f10ae2f8e0.1730709384.git.stano.jakubek@gmail.com
Signed-off-by: Lee Jones <lee@kernel.org>