added BRD2709A support

Author: Sarthak-Shaha

third_party/silabs/silabs_board.gni

@@ -25,7 +25,7 @@ declare_args() {
   silabs_mcu = ""
 
   # LCD is enabled by default
-  # Boards BRD4166A, BRD2601B, BRD2703A and BRD4319A do not have a LCD so they disable it explicitly
+  # Boards BRD4166A, BRD2601B, BRD2703A, BRD2709A and BRD4319A do not have a LCD so they disable it explicitly
   disable_lcd = false
 
   # Enable Buttons by default
@@ -178,7 +178,9 @@ if (silabs_board == "BRD4338A" || silabs_board == "BRD2605A" ||
   silabs_family = "efr32mg26"
   silabs_mcu = "EFR32MG26B510F3200IM48"
 
-  # BRD2709A do not have an external flash
+  # BRD2709A do not have an external flash and lcd
+  show_qr_code = false
+  disable_lcd = true
   use_external_flash = false
 } else if (silabs_board == "BRD4117A") {
   silabs_family = "efr32mg26"