leds: apu: extend support for PC Engines APU1 with newer firmware

The DMI_PRODUCT_NAME entry on current firmware of PC Engines APU1 changed
from "APU" to "apu1"

This modification adds the missing DMI data and thereby the LED support for
the PC Engines APU1 with firmware versions >= 4.6.8.

Signed-off-by: Andreas Eberlein <foodeas@aeberlein.de>
Tested-by: Zbyněk Kocur <zbynek.kocur@fel.cvut.cz>
Signed-off-by: Pavel Machek <pavel@ucw.cz>