led: add function naming option from linux

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>