modem: choice symbol for UART backend

Add a choice symbol that is used to select which UART backend to use.
This allows backends that don't use the interrupt API to be implemented.

Signed-off-by: Jordan Yates <jordan.yates@data61.csiro.au>

drivers/modem/CMakeLists.txt

@@ -10,7 +10,7 @@ zephyr_library_sources_ifdef(CONFIG_MODEM_CONTEXT
 	modem_pin.c
 )
 
-zephyr_library_sources_ifdef(CONFIG_MODEM_IFACE_UART modem_iface_uart.c)
+zephyr_library_sources_ifdef(CONFIG_MODEM_IFACE_UART_INTERRUPT modem_iface_uart_interrupt.c)
 zephyr_library_sources_ifdef(CONFIG_MODEM_CMD_HANDLER modem_cmd_handler.c)
 zephyr_library_sources_ifdef(CONFIG_MODEM_SOCKET modem_socket.c)
 

drivers/modem/Kconfig

@@ -64,8 +64,6 @@ config MODEM_CONTEXT_VERBOSE_DEBUG
 
 config MODEM_IFACE_UART
 	bool "UART-based modem interface"
-	depends on SERIAL_SUPPORT_INTERRUPT
-	select UART_INTERRUPT_DRIVEN
 	select RING_BUFFER
 	help
 	  To configure this layer for use, create a modem_iface_uart_data
@@ -73,6 +71,21 @@ config MODEM_IFACE_UART
 	  along with the modem_iface reference from your modem_context object
 	  and the UART device name.
 
+if MODEM_IFACE_UART
+
+choice MODEM_IFACE_UART_BACKEND
+	prompt "UART backend to use for modem interface"
+	default MODEM_IFACE_UART_INTERRUPT
+
+config MODEM_IFACE_UART_INTERRUPT
+	bool "UART-based modem interface using interrupt API"
+	depends on SERIAL_SUPPORT_INTERRUPT
+	select UART_INTERRUPT_DRIVEN
+
+endchoice
+
+endif # MODEM_IFACE_UART
+
 config MODEM_CMD_HANDLER
 	bool "Generic modem command handler"
 	select NET_BUF