STM32: Migrate variants to new structure

variants/stm32/CDEBYTE_E77-MBL/platformio.ini

@@ -5,7 +5,7 @@ board_upload.maximum_size = 233472 ; reserve the last 28KB for filesystem
 board_level = extra
 build_flags =
   ${stm32_base.build_flags}
-  -Ivariants/CDEBYTE_E77-MBL
+  -Ivariants/stm32/CDEBYTE_E77-MBL
   -DSERIAL_UART_INSTANCE=1
   -DPIN_SERIAL_RX=PA3
   -DPIN_SERIAL_TX=PA2

variants/stm32/rak3172/platformio.ini

@@ -4,7 +4,7 @@ board = wiscore_rak3172
 board_upload.maximum_size = 233472 ; reserve the last 28KB for filesystem
 build_flags =
   ${stm32_base.build_flags}
-  -Ivariants/rak3172
+  -Ivariants/stm32/rak3172
   -DPIN_WIRE_SDA=PA11
   -DPIN_WIRE_SCL=PA12
   -DMESHTASTIC_EXCLUDE_ENVIRONMENTAL_SENSOR=1

variants/stm32/wio-e5/platformio.ini

@@ -4,7 +4,7 @@ board = lora_e5_dev_board
 board_upload.maximum_size = 233472 ; reserve the last 28KB for filesystem
 build_flags =
   ${stm32_base.build_flags}
-  -Ivariants/wio-e5
+  -Ivariants/stm32/wio-e5
   -DSERIAL_UART_INSTANCE=1
   -DPIN_SERIAL_RX=PB7
   -DPIN_SERIAL_TX=PB6