Enable ext_intra by default

Change-Id: Id7a257fb56f2e435fadb9202f775c5d12fc1bea6

configure

diff --git a/configure b/configure
index 36d0ac3..3e7de78 100755
--- a/configure
+++ b/configure
@@ -483,6 +483,7 @@
     soft_enable cdef
     soft_enable ec_adapt
     soft_enable new_tokenset
+    soft_enable ext_intra
 
     # Backwards/jenkins compatibility with --enable-aom-highbitdepth
     enabled aom_highbitdepth && enable_feature highbitdepth