mesa: fix dependency

mesa: fix dependency

libudev is asked by enable-gbm, not enable_dri, and enable-gbm always is yes;

We can find the dependency from configure.ac codes:
	if test "x$enable_gbm" = xyes; then
	    SRC_DIRS="$SRC_DIRS gbm"

	    PKG_CHECK_MODULES([LIBUDEV], [libudev], [],
	                      AC_MSG_ERROR([gbm needs udev]))

	    if test "x$enable_dri" = xyes; then
	        GBM_BACKEND_DIRS="$GBM_BACKEND_DIRS dri"
	        if test "x$enable_shared_glapi" = xno; then
	            AC_MSG_ERROR([gbm_dri requires --enable-shared-glapi])
	        fi
	    fi
	fi

Signed-off-by: Roy Li <rongqing.li@windriver.com>
Signed-off-by: Saul Wold <sgw@linux.intel.com>