configs: qemu-riscv raise CONFIG_NR_DRAM_BANKS

configs: qemu-riscv raise CONFIG_NR_DRAM_BANKS

The number of memory banks in QEMU is not bounded by 1.

In this example we have two banks:

    qemu-system-riscv64 \
    -machine virt \
    -nographic \
    -m 8192 \
    -smp 8,sockets=2,cores=4,threads=1 \
    -numa node,cpus=0-3,mem=4096 \
    -numa node,cpus=4-7,mem=4096 \
    -kernel u-boot

As we will see RISC-V NUMA systems using U-Boot
we should be able to emulate these.

Use the default value defined in /Kconfig as 4.

Reviewed-by: Leo Yu-Chi Liang <ycliang@andestech.com>
Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>