Seperate FILTER_INTRA from EXT_INTRA experiment

Prepare for the av1/nextgenv2 merge.

Coding gain (%):

               lowres     midres
ext-intra       0.69       0.97
filter-intra    0.67       0.83
both            1.05       1.48

Change-Id: Ia24d6fafb3e484c4f92192e0b7eee5e39f4f4ee6
diff --git a/av1/av1_common.mk b/av1/av1_common.mk
index 29b71f3..d8f805f 100644
--- a/av1/av1_common.mk
+++ b/av1/av1_common.mk
@@ -139,7 +139,7 @@
 AV1_COMMON_SRCS-$(HAVE_NEON) += common/arm/neon/iht8x8_add_neon.c
 endif
 
-ifeq ($(CONFIG_EXT_INTRA),yes)
+ifeq ($(CONFIG_FILTER_INTRA),yes)
 AV1_COMMON_SRCS-yes += common/intra_filters.h
 AV1_COMMON_SRCS-$(HAVE_SSE4_1) += common/x86/reconintra_sse4.c
 endif