leds: add new LED_FUNCTION_PLAYER for player LEDs for game controllers.

Player LEDs are commonly found on game controllers from Nintendo and Sony
to indicate a player ID across a number of LEDs. For example, "Player 2"
might be indicated as "-x--" on a device with 4 LEDs where "x" means on.

This patch introduces LED_FUNCTION_PLAYER1-5 defines to properly indicate
player LEDs from the kernel. Until now there was no good standard, which
resulted in inconsistent behavior across xpad, hid-sony, hid-wiimote and
other drivers. Moving forward new drivers should use LED_FUNCTION_PLAYERx.

Note: management of Player IDs is left to user space, though a kernel
driver may pick a default value.

Signed-off-by: Roderick Colenbrander <roderick.colenbrander@sony.com>
Acked-by: Pavel Machek <pavel@ucw.cz>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>