package/libcamera-apps: enable LIBAV only if libdrm and ffmpeg is present

Since commit 35266e84043f880d7591e52b71a8c5b8d0e4717d, libcamera-apps
does enable LIBAV by default which depends on libdrm and ffpmeg.

Fixes:
- http://autobuild.buildroot.net/results/548f2a3b353ce4693fb60d7fb1e06e02af22991c/

/home/buildroot/autobuild/run/instance-1/output-1/build/libcamera-apps-1.1.1/encoder/libav_encoder.cpp:13:10: fatal error: libdrm/drm_fourcc.h: No such file or directory
   13 | #include <libdrm/drm_fourcc.h>
      |          ^~~~~~~~~~~~~~~~~~~~~

Signed-off-by: Marcus Folkesson <marcus.folkesson@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/libcamera-apps/libcamera-apps.mk

@@ -29,6 +29,13 @@ else
 LIBCAMERA_APPS_CONF_OPTS += -DENABLE_DRM=0
 endif
 
+ifeq ($(BR2_PACKAGE_FFMPEG)$(BR2_PACKAGE_LIBDRM),yy)
+LIBCAMERA_APPS_DEPENDENCIES += ffmpeg libdrm
+LIBCAMERA_APPS_CONF_OPTS += -DENABLE_LIBAV=1
+else
+LIBCAMERA_APPS_CONF_OPTS += -DENABLE_LIBAV=0
+endif
+
 ifeq ($(BR2_PACKAGE_XORG7),y)
 LIBCAMERA_APPS_DEPENDENCIES += \
 	$(if $(BR2_PACKAGE_LIBEPOXY),libepoxy) \