tests/avocado: use default amount of cores on sbsa-ref

tests/avocado: use default amount of cores on sbsa-ref

The version of the sbsa-ref EDK2 firmware we used to use in this test
had a bug where it might make an unaligned access to the framebuffer,
which causes a guest crash on newer versions of QEMU where we enforce
the architectural requirement that unaligned accesses to Device memory
should take an exception.

We happened to not notice this because our test was booting with "-smp
1" and through luck this didn't write the boot logo to the framebuffer
at an unaligned address; but trying to boot the same firmware with two
CPUs would result in a guest crash. Now we have updated the firmware
we're using for the test, we can make the test use all the cores on the
board, so we are testing the SMP boot path.

Signed-off-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-id: 20240620-b4-new-firmware-v3-2-29a3a2f1be1e@linaro.org
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>