configs: fix, simplify RADEON_LIBS, RADEON_CFLAGS

Fixes build problems with the r200, radeon drivers.

NOTE: This is a candidate for the 8.0 branch.
diff --git a/configs/linux-dri b/configs/linux-dri
index 6990c3a..e63790e 100644
--- a/configs/linux-dri
+++ b/configs/linux-dri
@@ -70,7 +70,6 @@
 NOUVEAU_LIBS = $(shell $(PKG_CONFIG) --libs libdrm_nouveau)
 NOUVEAU_CFLAGS = $(shell $(PKG_CONFIG) --cflags libdrm_nouveau)
 
-LIBDRM_RADEON_LIBS = $(shell $(PKG_CONFIG) --libs libdrm_radeon)
-LIBDRM_RADEON_CFLAGS = $(shell $(PKG_CONFIG) --cflags libdrm_radeon)
-RADEON_CFLAGS = "-DHAVE_LIBDRM_RADEON=1 $(LIBDRM_RADEON_CFLAGS)"
+RADEON_LIBS = $(shell $(PKG_CONFIG) --libs libdrm_radeon)
+RADEON_CFLAGS = $(shell $(PKG_CONFIG) --cflags libdrm_radeon)
 RADEON_LDFLAGS = $(LIBDRM_RADEON_LIBS)