tests/avocado: Add set of boot tests on SBSA-ref

tests/avocado: Add set of boot tests on SBSA-ref

This change adds set of boot tests on SBSA-ref machine:

1. boot firmware up to the EDK2 banner
2. boot Alpine Linux

Prebuilt flash volumes are included, built using upstream documentation.

To unify tests for AArch64/virt and AArch64/sbsa-ref we boot
the same Alpine Linux image on both.

Signed-off-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20230323082813.971535-1-marcin.juszkiewicz@linaro.org>
Reviewed-by: Leif Lindholm <quic_llindhol@quicinc.com>
Message-Id: <20230328171426.14258-1-philmd@linaro.org>
Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Message-Id: <20230424092249.58552-4-alex.bennee@linaro.org>