leds: leds-alix2c - take port address from MSR

This makes the LEDs driver for ALIX2.C boards work with Coreboot by
looking up the port address in the MSR rather than hard-coding it.

The BIOS scan also needed some tweaks as the string in Coreboot differs
from the one in the legacy BIOS.

Successfully tested with both the legacy tinyBIOS as well as Coreboot
v3.

Signed-off-by: Daniel Mack <daniel@caiaq.de>
Signed-off-by: Richard Purdie <rpurdie@linux.intel.com>