Disable angle opengl in embedded linux

Angle opengl has dependency to mesa (libdrm/gbm), but component
is never built on embedded linux. Disable to avoid unnecessary
check.

Change-Id: Ie1e2ef56692f5e311bb2011a15dba9de1bb8de2f
Reviewed-by: Allan Sandfeld Jensen <allan.jensen@qt.io>

src/core/config/embedded_linux.pri

@@ -39,5 +39,6 @@ GYP_CONFIG += \
     use_x11=0 \
     v8_use_snapshot=false \
     want_separate_host_toolset=1 \
+    angle_enable_gl=0 \
 
 WEBENGINE_CONFIG *= reduce_binary_size