TT#108000 Implement getPref function in DeviceConfig

* getPref will help retrieve exactly the preference
	    by name, or return a default value if preference
	    is not found; it should simplify device configs
	    a lot

Change-Id: I8e730b2f51a7819a39956879bff6cf771fb6132b
(cherry picked from commit a61d4db5b6)

lib/NGCP/Panel/Template/Plugin/DeviceConfig.pm

@@ -39,4 +39,18 @@ sub getValue {
   return;
 }
 
+sub getPref {
+  my $self = shift;
+  my ($pref_name, $default_val) = @_;
+
+  my $preferences = $self->{_CONTEXT}->stash->get('preferences');
+  foreach my $level (qw/device profile model/) {
+    my $v = $preferences->{device}->{$level}->{$pref_name};
+    next unless $v;
+    return $v;
+  }
+
+  return $default_val // '';
+}
+
 1;