Lua -- Fix device hang when scroll function active on clear_screen

I previously noticed that manually clearing the framebuffer while scroll
function was active caused lua to crash

I could reproduce in sim and on device but I thought using the plugin
supplied rb->lcd_clear_screen was immune to this issue

Unfortunately some devices exhibit this behavior with the plugin function
as well

This patch adds rb->lcd_scroll_stop() before lcd_clear_screen at lua start-up
and to the supplied include file lcd.lua

Change-Id: I9800145e5c834ea27df5db5f1bca50b0d40faa49

apps/plugins/lua/rocklua.c

@@ -160,6 +160,7 @@ enum plugin_status plugin_start(const void* parameter)
         rocklua_openlibs(L);
         status = luaL_loadfile(L, filename);
         if (!status) {
+            rb->lcd_scroll_stop(); /* rb doesn't like bg change while scroll */
             rb->lcd_clear_display();
             status = docall(L);
         }