DT: leds: Improve description of flash LEDs related properties
DT: leds: Improve description of flash LEDs related properties

1. Since max-microamp property has had no users so far, then rename
   it to more descriptive led-max-microamp.
2. Since flash-timeout-us property has had no users so far, then rename
   it to more accurate flash-max-timeout-us.
3. Describe led-max-microamp property as mandatory for specific board
   configurations.
4. Make flash-max-microamp and flash-max-timeout-us properties mandatory
   for devices with configurable flash current and flash timeout settings
   respectively.

Signed-off-by: Jacek Anaszewski <6a953cb1c532e2765a42e582ecefff5a01106214@samsung.com>
Cc: Richard Purdie <a03894c799ea916bd571ce8f12ed88f6fb3400f7@rpsys.net>
Cc: Pavel Machek <2375fa63e2908bb2df59f606483a3aa92321db7a@ucw.cz>
Cc: eb682e570f95b554c8a7dc560ee59b91b930a718@vger.kernel.org
Acked-by: Sakari Ailus <8d98c2be02a446df653daa2c00496b87f3f016e4@linux.intel.com>
Acked-by: Sylwester Nawrocki <1ca386fdc5066df13f7236f0837f22126191d06b@samsung.com>

KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs,KristFoundation/Programs