riscv: defconfig: enable BLK_DEV_NVME

NVMe is a non-volatile storage media attached via PCIe.
As NVMe has much higher throughput than other block devices like
SATA it is a must have for RISC-V. Enable CONFIG_BLK_DEV_NVME.

The HiFive Unmatched is a board providing M.2 slots for NVMe drives.
Enable CONFIG_PCIE_FU740.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Anup Patel <anup@brainfault.org>
Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>