ARM: shmobile: defconfig: Refresh for v6.4-rc1

Refresh the defconfig for Renesas ARM systems:
  - Move CONFIG_PCI_RCAR_GEN2=y (moved in commit 81c362e7
    ("PCI: Sort controller Kconfig entries by vendor")),
  - Drop CONFIG_SERIAL_8250_PCI1XXXX=n (no longer auto-enabled since
    commit 5d943b5d ("serial: 8250_pci1xxxx: Disable
    SERIAL_8250_PCI1XXXX config by default")).

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/420669d925bf4a8527c80dd294568df3b0556058.1683705341.git.geert+renesas@glider.be