leds: sy7802: Add support for Silergy SY7802 flash LED controller

The SY7802 is a current-regulated charge pump which can regulate two
current levels for Flash and Torch modes.

It is a high-current synchronous boost converter with 2-channel high
side current sources. Each channel is able to deliver 900mA current.

Acked-by: Lee Jones <lee@kernel.org>
Signed-off-by: André Apitzsch <git@apitzsch.eu>
Link: https://lore.kernel.org/r/20240624-sy7802-v5-2-7abc9d96bfa6@apitzsch.eu


Signed-off-by: Lee Jones <lee@kernel.org>