hw/riscv: Add the checking if DTB overlaps to kernel or initrd

hw/riscv: Add the checking if DTB overlaps to kernel or initrd

DTB is placed to the end of memory, so we will check if the start
address of DTB overlaps to the address of kernel/initrd.

Signed-off-by: Jim Shu <jim.shu@sifive.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20241120153935.24706-4-jim.shu@sifive.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>