dm: led: Tidy up SPL options for the led and led-gpio

At present SPL does not have its own option. But these features can
increase SPL code size. Adjust the Kconfig and Makefile so that
separate a SPL option can be selected.

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

drivers/led/Kconfig

@@ -11,7 +11,7 @@ config LED
 
 config SPL_LED
 	bool "Enable LED support in SPL"
-	depends on LED
+	depends on SPL && SPL_DM
 	help
 	  The LED subsystem adds a small amount of overhead to the image.
 	  If this is acceptable and you have a need to use LEDs in SPL,
@@ -27,4 +27,11 @@ config LED_GPIO
 	  The GPIO driver must used driver model. LEDs are configured using
 	  the device tree.
 
+config SPL_LED_GPIO
+	bool "LED support for GPIO-connected LEDs in SPL"
+        depends on SPL_LED && DM_GPIO
+	help
+	  This option is an SPL-variant of the LED_GPIO option.
+	  See the help of LED_GPIO for details.
+
 endmenu

drivers/led/Makefile

@@ -5,5 +5,5 @@
 # SPDX-License-Identifier:	GPL-2.0+
 #
 
-obj-$(CONFIG_LED) += led-uclass.o
-obj-$(CONFIG_LED_GPIO) += led_gpio.o
+obj-y += led-uclass.o
+obj-$(CONFIG_$(SPL_)LED_GPIO) += led_gpio.o