tests: acpi: simplify rsdt handling

tests: acpi: simplify rsdt handling

RSDT referenced tables always have length at offset 4 and checksum at
offset 9, that's enough for reusing fetch_table() and replacing custom
RSDT fetching code with it.
While at it
 * merge fetch_rsdt_referenced_tables() into test_acpi_rsdt_table()
 * drop test_data::rsdt_table/rsdt_tables_addr/rsdt_tables_nr since
   we need this data only for duration of test_acpi_rsdt_table() to
   fetch other tables and use locals instead.

Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Acked-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>