Move use_rps_extension arg declaration so users can overwritte de default value and skip it rps creation (#31255)

diff --git a/third_party/silabs/silabs_board.gni b/third_party/silabs/silabs_board.gni
index dd34fc6..c052ef5 100644
--- a/third_party/silabs/silabs_board.gni
+++ b/third_party/silabs/silabs_board.gni
@@ -51,9 +51,6 @@
 
   # Self-provision enabled
   use_provision_channel = false
-
-  # Board required .rps file to flash instead of .s37
-  use_rps_extension = false
 }
 
 declare_args() {
@@ -114,7 +111,6 @@
   show_qr_code = false
   wifi_soc = true
   silabs_board_lower = "brd4325b"
-  use_rps_extension = true
 } else if (silabs_board == "BRD4325C") {
   silabs_family = "SiWx917-common"
   silabs_mcu = "SiWG917M111MGTBA"
@@ -123,7 +119,6 @@
   wifi_soc = true
   wifi_soc_common_flash = true
   silabs_board_lower = "brd4325c"
-  use_rps_extension = true
 } else if (silabs_board == "BRD4325G") {
   silabs_family = "SiWx917-common"
   silabs_mcu = "SiWG917M111MGTBA"
@@ -132,7 +127,6 @@
   wifi_soc = true
   wifi_soc_common_flash = true
   silabs_board_lower = "brd4325g"
-  use_rps_extension = true
 } else if (silabs_board == "BRD4338A") {
   silabs_family = "SiWx917-common"
   silabs_mcu = "SiWG917M111MGTBA"
@@ -141,7 +135,6 @@
   wifi_soc = true
   wifi_soc_common_flash = true
   silabs_board_lower = "brd4338a"
-  use_rps_extension = true
 } else if (silabs_board == "BRD4180A") {
   assert(
       false,
@@ -216,5 +209,13 @@
       "The board ${silabs_board} is unsupported. A list of supported board can be found here https://t.ly/_b3SK")
 }
 
+declare_args() {
+  # Wifi SoC Board require a .rps file to be flashed to the device to run
+  # this rps file is created from the built binary but it requires Silabs Commander tool
+  # User can set this arg to false to skip the rps creation for WiFi SoCs.
+  # e.g. for CI
+  use_rps_extension = wifi_soc
+}
+
 # qr code cannot be true if lcd is disabled
 assert(!(disable_lcd && show_qr_code))