mfd: Add support for AAEON UP board FPGA

mfd: Add support for AAEON UP board FPGA

The UP boards implement some features (pin controller, LEDs) through an
on-board FPGA.

This MFD driver implements the line protocol to communicate with the FPGA
through regmap, and registers pin controller and led cells.

This commit adds support for UP and UP Squared boards.

Based on the work done by Gary Wang <garywang@aaeon.com.tw>.

Signed-off-by: Thomas Richard <thomas.richard@bootlin.com>
Link: https://lore.kernel.org/r/20241211-aaeon-up-board-pinctrl-support-v1-1-24719be27631@bootlin.com
Signed-off-by: Lee Jones <lee@kernel.org>