tests/acpi: don't pack a structure

tests/acpi: don't pack a structure

There's no reason to pack structures where we don't care about size or
padding, this applies to AcpiStdTable in tests/acpi-utils.h.

OTOH bios-tables-test happens to be passing the address of a field in
this  struct to a function that expects a pointer to normally aligned
data which results in a SIGBUS on architectures like SPARC that have
strict alignment requirements.

Fixes: 9e8458c02 ("acpi unit-test: compare DSDT and SSDT tables against expected values")
Reported-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Tested-by: Peter Maydell <peter.maydell@linaro.org>