radeonsi: Convert to automake

Can't use LTLIBRARIES here yet, since libradeon isn't converted.
diff --git a/configure.ac b/configure.ac
index ee36528..05dbc73 100644
--- a/configure.ac
+++ b/configure.ac
@@ -2018,6 +2018,7 @@
 		src/gallium/drivers/nvc0/Makefile
 		src/gallium/drivers/r300/Makefile
 		src/gallium/drivers/r600/Makefile
+		src/gallium/drivers/radeonsi/Makefile
 		src/gallium/drivers/rbug/Makefile
 		src/gallium/drivers/softpipe/Makefile
 		src/gallium/drivers/svga/Makefile