Check CONFIG_VP<N> instead of encoder and decoder

If either the encoder or the decoder is enabled, CONFIG_VP<N> will be
set. This simplifies the conditional and passes the chromium update
script when CONFIG_ values are passed in with 'yes' and 'no' values.

This was failing because it was checking against empty strings but
they are set to 'no'

Change-Id: I02ecd557210088ba1458cd0e89eead5666f6597a

libs.mk

diff --git a/libs.mk b/libs.mk
index b9d4b28..811a6e5 100644
--- a/libs.mk
+++ b/libs.mk
@@ -76,7 +76,7 @@
   CODEC_DOC_SECTIONS += vp8 vp8_decoder
 endif
 
-ifneq ($(CONFIG_VP9_ENCODER)$(CONFIG_VP9_DECODER),)
+ifeq ($(CONFIG_VP9),yes)
   VP9_PREFIX=vp9/
   include $(SRC_PATH_BARE)/$(VP9_PREFIX)vp9_common.mk
 endif
@@ -110,7 +110,7 @@
 $(BUILD_PFX)$(VP9_PREFIX)%.c.o: CFLAGS += -Wextra
 
 #  VP10 make file
-ifneq ($(CONFIG_VP10_ENCODER)$(CONFIG_VP10_DECODER),)
+ifeq ($(CONFIG_VP10),yes)
   VP10_PREFIX=vp10/
   include $(SRC_PATH_BARE)/$(VP10_PREFIX)vp10_common.mk
 endif