leds: Introduce the multi_max_intensity sysfs attribute

Some multicolor LEDs support global brightness control in hardware,
meaning that the maximum intensity of the color components is not
connected to the maximum global brightness. Such LEDs cannot be
described properly by the current multicolor LED class interface,
because it assumes that the maximum intensity of each color component
is described by the maximum global brightness of the LED.

Fix this by introducing a new sysfs attribute called
"multi_max_intensity" holding the maximum intensity values for the
color components of a multicolor LED class device. Drivers can use
the new max_intensity field inside struct mc_subled to tell the
multicolor LED class code about those values. Intensity values written
by userspace applications will be limited to this maximum value.

Drivers for multicolor LEDs that do not support global brightness
control in hardware might still want to use the maximum global LED
brightness supplied via devicetree as the maximum intensity of each
individual color component. Such drivers should set max_intensity
to 0 so that the multicolor LED core can act accordingly.

The lp50xx and ncp5623 LED drivers already use hardware-based control
for the global LED brightness. Modify those drivers to correctly
initalize .max_intensity to avoid being limited to the maximum global
brightness supplied via devicetree.

Reviewed-by: Werner Sembach <wse@tuxedocomputers.com>
Reviewed-by: Jacek Anaszewski <jacek.anaszewski@gmail.com>
Signed-off-by: Armin Wolf <W_Armin@gmx.de>
Link: https://patch.msgid.link/20260509214603.262368-2-W_Armin@gmx.de
Signed-off-by: Lee Jones <lee@kernel.org>

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