riscv: dts: spacemit: Add USB2 PHY node for K1

riscv: dts: spacemit: Add USB2 PHY node for K1

K1's DWC3 USB 3.0 controller requires two separate PHYs to function:
the USB 3.0 combophy (for SuperSpeed) and a USB 2.0 PHY (for High-Speed,
Full-Speed, etc.).

Add node for this second USB 2.0 PHY (usbphy2).

Tested-by: Aurelien Jarno <aurelien@aurel32.net>
Signed-off-by: Ze Huang <huang.ze@linux.dev>
Reviewed-by: Yixun Lan <dlan@gentoo.org>
Link: https://lore.kernel.org/r/20260111-k1-usb3dts-v2-v3-1-f5ebd546e904@linux.dev
Signed-off-by: Yixun Lan <dlan@gentoo.org>