led: add function naming option from linux

in linux we have the option to create the name of a led
optionally through the following properties:

- function
- color
- function-enumerator

This patch adds support for parsing this properties if there
is no label property.

The led name is created in led_post_bind() and we need some
storage place for it. Currently this patch prevents to use
malloc() instead it stores the name in new member :

        char name[LED_MAX_NAME_SIZE];

of struct led_uc_plat. While at it append led tests for the
new feature.

Signed-off-by: Heiko Schocher <hs@denx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>

include/led.h

@@ -53,6 +53,11 @@
 
 struct udevice;
 
+/*
+ * value imported from linux:include/linux/uapi/linux/uleds.h
+ */
+#define LED_MAX_NAME_SIZE      64
+
 enum led_state_t {
 	LEDST_OFF = 0,
 	LEDST_ON = 1,
@@ -86,6 +91,7 @@ struct led_sw_blink {
 struct led_uc_plat {
 	const char *label;
 	enum led_state_t default_state;
+	char name[LED_MAX_NAME_SIZE];
 #ifdef CONFIG_LED_SW_BLINK
 	struct led_sw_blink *sw_blink;
 #endif