dt-bindings: imx: gpcv2: add support for optional resets

For some domains the resets of the devices in the domain are not
automatically triggered. Add an optional resets property to allow
the GPC driver to trigger those resets explicitly.

The resets belong to devices located inside the power domain,
which need to be held in reset across the power-up sequence. So we
have no means to specify what each reset is in a generic power-domain
binding. Same situation as with the clocks in this binding actually.

Tested-by: Frieder Schrempf <frieder.schrempf@kontron.de>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Signed-off-by: Peng Fan <peng.fan@nxp.com>
Reviewed-by: Rob Herring <robh@kernel.org>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>