leds: Add missing includes and forward declarations in leds.h

Add missing includes and forward declarations to leds.h. While at it,
replace headers by forward declarations and vise versa.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Lee Jones <lee@kernel.org>
Link: https://lore.kernel.org/r/20230103131256.33894-2-andriy.shevchenko@linux.intel.com