drivers: gpio: ht16k33: add GPIO driver for Holtek HT16K33 LED driver

The HT16K33 is a memory mapping, multifunction LED controller
driver. The controller supports up to 128 LEDs (up to 16 rows and 8
commons) and matrix key scan circuit of up to 13x3 keys.

This commit adds support for the keyscan functionality of the HT16K33.

Signed-off-by: Henrik Brix Andersen <henrik@brixandersen.dk>