Make rpi video cross-compiler friendly.

* Stops using fixed path to find GLES/EGL libs.
* Tries pkg-config to locate bcm_host.

Signed-off-by: Guillermo A. Amaral <g@maral.me>

configure.in

@@ -1571,7 +1571,11 @@ CheckRPI()
 AC_HELP_STRING([--enable-video-rpi], [use Raspberry Pi video driver [[default=yes]]]),
                   , enable_video_rpi=yes)
     if test x$enable_video = xyes -a x$enable_video_rpi = xyes; then
-        if test x$ARCH = xnetbsd; then
+        AC_PATH_PROG(PKG_CONFIG, pkg-config, no)
+        if test x$PKG_CONFIG != xno && $PKG_CONFIG --exists bcm_host; then
+            RPI_CFLAGS=`$PKG_CONFIG --cflags bcm_host brcmegl`
+            RPI_LDFLAGS=`$PKG_CONFIG --libs bcm_host brcmegl`
+        elif test x$ARCH = xnetbsd; then
             RPI_CFLAGS="-I/usr/pkg/include -I/usr/pkg/include/interface/vcos/pthreads -I/usr/pkg/include/interface/vmcs_host/linux"
             RPI_LDFLAGS="-Wl,-R/usr/pkg/lib -L/usr/pkg/lib -lbcm_host"
         else