leds: pca955x: Add HW blink support

leds: pca955x: Add HW blink support

Support blinking using the PCA955x chip. Use PWM0 for blinking
instead of LED_HALF brightness. Since there is only one frequency
and brightness register for any blinking LED, track the blink state
of each LED and only support one HW blinking frequency. If another
frequency is requested, fallback to software blinking. In addition,
blinked LEDs can only use full brightness in order to maintain 50%
duty cycle, which is required for the specified blink rate.

Signed-off-by: Eddie James <eajames@linux.ibm.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Link: https://lore.kernel.org/r/20250212143038.1416501-5-eajames@linux.ibm.com
Signed-off-by: Lee Jones <lee@kernel.org>