riscv/sifive_u: Add the start-in-flash property

Add a property that when set to true QEMU will jump from the ROM code to
the start of flash memory instead of DRAM which is the default
behaviour.

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/sifive_u.h

@@ -57,6 +57,8 @@ typedef struct SiFiveUState {
 
     void *fdt;
     int fdt_size;
+
+    bool start_in_flash;
 } SiFiveUState;
 
 enum {