ac, radeonsi: automake: add missing builddir include

The generated file is correctly stored in the builddir as of earlier
commit. Yet the commit forgot to add the respective include flag thus
the compiler would error out failing to find sid_tables.h

Bugzila: https://bugs.freedesktop.org/show_bug.cgi?id=99389
Fixes: d1dc22eb466 "ac: automake: rework sid_tables.h generation"
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>
2 files changed