svc_encoder_rtc: don't include internal encoder.h

svc_encoder_rtc.c should only use libaom's public API, so remove the
inclusion of the internal header av1/encoder/encoder.h. To compensate
for that, include the following headers.

Include <limits.h> for the definition of INT_MAX.

Include aom/aom_decoder.h if CONFIG_AV1_DECODER is defined. Include
config/aom_config.h for the definition of CONFIG_AV1_DECODER.

Include aom_ports/bitops.h for the definition of static inline function
get_msb().

Bug: aomedia:3404
Bug: aomedia:3417
Change-Id: Ibc1f9d1e4f0f5991b79c1b5bb18671ebde426cac
diff --git a/examples/svc_encoder_rtc.c b/examples/svc_encoder_rtc.c
index b6408dc..485d5a8 100644
--- a/examples/svc_encoder_rtc.c
+++ b/examples/svc_encoder_rtc.c
@@ -12,20 +12,26 @@
 //  encoding scheme for RTC video applications.
 
 #include <assert.h>
+#include <limits.h>
 #include <math.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
 
+#include "config/aom_config.h"
+
+#if CONFIG_AV1_DECODER
+#include "aom/aom_decoder.h"
+#endif
 #include "aom/aom_encoder.h"
 #include "aom/aomcx.h"
 #include "av1/common/enums.h"
-#include "av1/encoder/encoder.h"
 #include "common/args.h"
 #include "common/tools_common.h"
 #include "common/video_writer.h"
 #include "examples/encoder_util.h"
 #include "aom_ports/aom_timer.h"
+#include "aom_ports/bitops.h"
 
 #define OPTION_BUFFER_SIZE 1024