Follow-up to commit e36ddf3226864e09 ("riscv: defconfig: Disable RZ/Five
peripheral support") in v6.12-rc1:
- Disable ARCH_RENESAS, too, as currently RZ/Five is the sole Renesas
RISC-V SoC,
- Drop no longer needed explicit disable of USB_XHCI_RCAR, which
depends on ARCH_RENESAS.