dts: bindings: serial: pl011: Make included `reset-device.yaml`

The PL011 driver has already implemented supporting reset device
behavior.
However, the support is incomplete because the `arm,pl011.yaml`,
does not contain a `reset-device.yaml`.

Add include directive to `arm,pl011.yaml` to including
`reset-device.yaml` to complete the support for reset device.

Signed-off-by: TOKITA Hiroshi <tokita.hiroshi@gmail.com>