dt-bindings: leds: adopt Linux PCA9532 binding constants

I'm working on a v2 patch to add support for a board named pdu001. Its
Linux DTS file uses the include file added by this patch. To keep Linux
and U-Boot DTS files in sync U-Boot requires a copy of this file,
although there is no driver for NXP's PCA9532 i2c LED driver chip (yet).

Signed-off-by: Felix Brack <fb@ltec.ch>