riscv: dts: starfive: beaglev-starlight: Setup phy reset gpio

The BeagleV Starlight SBC uses a Microchip KSZ9031RNXCA PHY supporting
RGMII-ID which doesn't require any particular setup, other than defining
a reset gpio, as opposed to VisionFive V1 for which the RX internal
delay had to be adjusted.

Co-developed-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Reviewed-by: Jacob Keller <jacob.e.keller@intel.com>
Reviewed-by: Emil Renner Berthing <emil.renner.berthing@canonical.com>
Signed-off-by: Conor Dooley <conor.dooley@microchip.com>