hw/riscv/virt: Add memmap pointer to RiscVVirtState

hw/riscv/virt: Add memmap pointer to RiscVVirtState

memmap needs to be exported outside of virt.c so that
modules like acpi can use it. Hence, add a pointer field
in RiscVVirtState structure and initialize it with the
memorymap.

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Reviewed-by: Bin Meng <bmeng@tinylab.org>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Message-ID: <20230302091212.999767-4-sunilvl@ventanamicro.com>
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>