Fix -Wmissing-declarations fft_avx2.c fft_sse2.c.

Add #include "config/aom_dsp_rtcd.h" to fix all -Wmissing-declarations
warnings in aom_dsp/x86/fft_avx2.c and most -Wmissing-declarations
warnings in aom_dsp/x86/fft_sse2.c

Change-Id: Ifd75fa58a2c3f82393ff09a768b478e09ca67b10
diff --git a/aom_dsp/x86/fft_avx2.c b/aom_dsp/x86/fft_avx2.c
index 54da022..4cccc5f 100644
--- a/aom_dsp/x86/fft_avx2.c
+++ b/aom_dsp/x86/fft_avx2.c
@@ -11,6 +11,7 @@
 
 #include <immintrin.h>
 
+#include "config/aom_dsp_rtcd.h"
 #include "aom_dsp/aom_dsp_common.h"
 #include "aom_dsp/fft_common.h"
 
diff --git a/aom_dsp/x86/fft_sse2.c b/aom_dsp/x86/fft_sse2.c
index 12bdc3e..6f20a3c 100644
--- a/aom_dsp/x86/fft_sse2.c
+++ b/aom_dsp/x86/fft_sse2.c
@@ -11,6 +11,7 @@
 
 #include <xmmintrin.h>
 
+#include "config/aom_dsp_rtcd.h"
 #include "aom_dsp/aom_dsp_common.h"
 #include "aom_dsp/fft_common.h"