dm: serial: Allow driver-model serial to be disabled for TPL

Add separate enable/disable controls for driver-model serial. While this
is generally enabled in SPL it may not be in TPL, since serial output can
be obtained with the debug UART with minimal code size.

Signed-off-by: Simon Glass <sjg@chromium.org>

drivers/serial/Kconfig

@@ -53,6 +53,26 @@ config DM_SERIAL
 	  implements serial_putc() etc. The uclass interface is
 	  defined in include/serial.h.
 
+config SPL_DM_SERIAL
+	bool "Enable Driver Model for serial drivers"
+	depends on DM_SERIAL
+	default y if SPL && DM_SERIAL
+	help
+	  Enable driver model for serial in SPL. This replaces
+	  drivers/serial/serial.c with the serial uclass, which
+	  implements serial_putc() etc. The uclass interface is
+	  defined in include/serial.h.
+
+config TPL_DM_SERIAL
+	bool "Enable Driver Model for serial drivers"
+	depends on DM_SERIAL
+	default y if TPL && DM_SERIAL
+	help
+	  Enable driver model for serial in TPL. This replaces
+	  drivers/serial/serial.c with the serial uclass, which
+	  implements serial_putc() etc. The uclass interface is
+	  defined in include/serial.h.
+
 config DEBUG_UART
 	bool "Enable an early debug UART for debugging"
 	help

drivers/serial/Makefile

@@ -6,7 +6,7 @@
 #
 
 ifdef CONFIG_DM_SERIAL
-obj-y += serial-uclass.o
+obj-$(CONFIG_$(SPL_TPL_)DM_SERIAL) += serial-uclass.o
 obj-$(CONFIG_PL01X_SERIAL) += serial_pl01x.o
 else
 obj-y += serial.o