At present the HTIF proxy syscall is unsupported. On RV32, only
device 0 is supported so there is no console device for RV32.
The only way to implement console funtionality on RV32 is to
support the SYS_WRITE syscall.

With this commit, the Spike machine is able to boot the 32-bit
OpenSBI generic image.

Signed-off-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20221229091828.1945072-8-bmeng@tinylab.org>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>