wifi: wilc1000: add function to read mac address from eFuse

wilc driver currently reads and sets mac address by firmware calls. It
means that we can not access mac address if no interface has been brought
up (so firmware is up and running). Another way to get mac address is to
read it directly from eFUSE.

Add a function helper to read the mac address written in eFuse, without
firmware assistance

Signed-off-by: Alexis Lothoré <alexis.lothore@bootlin.com>
Signed-off-by: Kalle Valo <kvalo@kernel.org>
Link: https://msgid.link/20240514-mac_addr_at_probe-v2-4-afef09f1cd10@bootlin.com