hw/riscv: Add support for loading a firmware

Add support for loading a firmware file for the virt machine and the
SiFive U. This can be run with the following command:

    qemu-system-riscv64 -machine virt -bios fw_jump.bin -kernel vmlinux

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
Tested-by: Bin Meng <bmeng.cn@gmail.com>
Signed-off-by: Palmer Dabbelt <palmer@sifive.com>

include/hw/riscv/boot.h

@@ -20,6 +20,8 @@
 #ifndef RISCV_BOOT_H
 #define RISCV_BOOT_H
 
+target_ulong riscv_load_firmware(const char *firmware_filename,
+                                 hwaddr firmware_load_addr);
 target_ulong riscv_load_kernel(const char *kernel_filename);
 hwaddr riscv_load_initrd(const char *filename, uint64_t mem_size,
                          uint64_t kernel_entry, hwaddr *start);