riscv: defconfig: Disable Renesas SoC support

Follow-up to commit e36ddf3 ("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.

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@bp.renesas.com>
Link: https://lore.kernel.org/r/e8a2fb273c8c68bd6d526b924b4212f397195b28.1738764211.git.geert+renesas@glider.be
Signed-off-by: Alexandre Ghiti <alexghiti@rivosinc.com>

arch/riscv/configs/defconfig

@@ -26,7 +26,6 @@ CONFIG_EXPERT=y
 # CONFIG_SYSFS_SYSCALL is not set
 CONFIG_PROFILING=y
 CONFIG_ARCH_MICROCHIP=y
-CONFIG_ARCH_RENESAS=y
 CONFIG_ARCH_SIFIVE=y
 CONFIG_ARCH_SOPHGO=y
 CONFIG_ARCH_SPACEMIT=y
@@ -202,7 +201,6 @@ CONFIG_USB=y
 CONFIG_USB_OTG=y
 CONFIG_USB_XHCI_HCD=y
 CONFIG_USB_XHCI_PLATFORM=y
-# CONFIG_USB_XHCI_RCAR is not set
 CONFIG_USB_EHCI_HCD=y
 CONFIG_USB_EHCI_HCD_PLATFORM=y
 CONFIG_USB_OHCI_HCD=y