Use ATTRIBUTE_PACKED for some more enums.

After this patch, they use 1 byte instead of 4 bytes.

BUG=aomedia:940

Change-Id: Id00f2a0618e458ba7fb985ecc10d581f156a18cd
diff --git a/av1/common/filter.h b/av1/common/filter.h
index c955aa7..2f1689a 100644
--- a/av1/common/filter.h
+++ b/av1/common/filter.h
@@ -29,7 +29,7 @@
 #define USE_12TAP_FILTER 0
 #define USE_EXTRA_FILTER 0
 
-typedef enum {
+typedef enum ATTRIBUTE_PACKED {
   EIGHTTAP_REGULAR,
   EIGHTTAP_SMOOTH,
 #if USE_EXTRA_FILTER