dt-bindings: power: Convert imx gpc to json-schema

Convert the i.MX GPC binding to DT schema format using json-schema

>From latest reference manual, there is actually ONLY 1 interrupt for
GPC, so the additional GPC interrupt is removed.

Consumer's example is also removed since it is NOT that useful.

Signed-off-by: Anson Huang <Anson.Huang@nxp.com>
Signed-off-by: Rob Herring <robh@kernel.org>