tests/avocado: add RISC-V OpenSBI boot test

tests/avocado: add RISC-V OpenSBI boot test

This test is used to do a quick sanity check to ensure that we're able
to run the existing QEMU FW image.

'sifive_u', 'spike' and 'virt' riscv64 machines, and 'sifive_u' and
'virt' 32 bit machines are able to run the default RISCV64_BIOS_BIN |
RISCV32_BIOS_BIN firmware with minimal options.

The riscv32 'spike' machine isn't bootable at this moment, requiring an
OpenSBI fix [1] and QEMU side changes [2]. We could just leave at that
or add a 'skip' test to remind us about it. To work as a reminder that
we have a riscv32 'spike' test that should be enabled as soon as OpenSBI
QEMU rom receives the fix, we're adding a 'skip' test:

(06/18) tests/avocado/riscv_opensbi.py:RiscvOpenSBI.test_riscv32_spike:
        SKIP: requires OpenSBI fix to work

[1] https://patchwork.ozlabs.org/project/opensbi/patch/20221226033603.1860569-1-bmeng@tinylab.org/
[2] https://patchwork.ozlabs.org/project/qemu-devel/list/?series=334159

Cc: Cleber Rosa <crosa@redhat.com>
Cc: Philippe Mathieu-Daudé <philmd@linaro.org>
Reviewed-by: Bin Meng <bmeng@tinylab.org>
Tested-by: Bin Meng <bmeng@tinylab.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230102115241.25733-2-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>