hw/riscv: sifive_u: Allow specifying the CPU

Allow the user to specify the main application CPU for the sifive_u
machine.

Signed-off-by: Alistair Francis <alistair.francis@wdc.com>
Reviewed-by: Bin Meng <bin.meng@windriver.com>
Reviewed-by: Palmer Dabbelt <palmerdabbelt@google.com>
Tested-by: Bin Meng <bin.meng@windriver.com>
Message-id: b8412086c8aea0eff30fb7a17f0acf2943381b6a.1602634524.git.alistair.francis@wdc.com
2 files changed