lights: Add LP5562 RGBLED driver

This adds support for the TI LP5562 RGB LED driver.

Things to note:
- The driver is initialized in simple PWM mode using its internal clock,
  for R,G,B, but not for W(hite).
- The chip doesn't have a WHO_AM_I or DEVICE_ID register to check.
  Instead we read the W_CURRENT register that we're generally not using
  and therefore doesn't get changed.
- The current is left at the default 17.5 mA but could be changed using
  the command line argument.

Datasheet:
https://www.ti.com/lit/ds/symlink/lp5562.pdf

Signed-off-by: Julian Oes <julian@oes.ch>

ROMFS/px4fmu_common/init.d/rcS

@@ -254,6 +254,7 @@ else
 	#
 	rgbled start -X -q
 	rgbled_ncp5623c start -X -q
+	rgbled_lp5562 start -X -q
 
 	#
 	# Override parameters from user configuration file.