RISC-V: defconfig: Enable Generic PCIE by default

Enable generic PCIe by default in the RISC-V defconfig, this allows us
to use QEMU's PCIe support out of the box.  CONFIG_RAS=y is
automatically selected by generic PCIe, so it has been dropped from
the defconfig.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
[Palmer: Split out PCIE_XILINX and CRYPTO_DEV_VIRTIO]
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>