sandbox: Allow building with GENERATE_ACPI_TABLE

At present this option is missing a header file, a function prototype and
the qfw driver needs a header included.

Fix these problems so we can enable this option on sandbox. This will
increase the build coverage.

Signed-off-by: Simon Glass <sjg@chromium.org>

arch/sandbox/include/asm/acpi_table.h

@@ -6,4 +6,6 @@
 #ifndef __ASM_ACPI_TABLE_H__
 #define __ASM_ACPI_TABLE_H__
 
+ulong write_acpi_tables(ulong start);
+
 #endif /* __ASM_ACPI_TABLE_H__ */