dt-bindings: leds: Add LED_FUNCTION_SPEED_* for link speed on LAN/WAN

Add LED_FUNCTION_SPEED_LAN and LED_FUNCTION_SPEED_WAN for LEDs that
indicate link speed of ethernet ports on LAN/WAN. This is useful to
distinguish those LEDs from LEDs that indicate link status (up/down).

example:

Fortinet FortiGate 30E/50E have LEDs that indicate link speed on each
of the ethernet ports in addition to LEDs that indicate link status
(up/down).

- 1000 Mbps: green:speed-(lan|wan)-N
- 100 Mbps: amber:speed-(lan|wan)-N
- 10 Mbps: (none, turned off)

Signed-off-by: INAGAKI Hiroshi <[e-mail]>
Reviewed-by: Rob Herring <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Lee Jones <[e-mail]>

include/dt-bindings/leds/common.h

···
 #define LED_FUNCTION_PROGRAMMING "programming"
 #define LED_FUNCTION_RX "rx"
 #define LED_FUNCTION_SD "sd"
+#define LED_FUNCTION_SPEED_LAN "speed-lan"
+#define LED_FUNCTION_SPEED_WAN "speed-wan"
 #define LED_FUNCTION_STANDBY "standby"
 #define LED_FUNCTION_TORCH "torch"
 #define LED_FUNCTION_TX "tx"