audio: Make pcspk card selectable again

audio: Make pcspk card selectable again

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Since we moved pcspk into hwlib, CONFIG_PCSPK is no longer defined per
target. Therefore, statically built soundhw array in arch_init.c stopped
including this card.

Work around this by re-adding this define to config-target.mak.
Long-term, a dynamic creation of this soundhw list will be necessary.

Signed-off-by: Jan Kiszka <jan.kiszka@siemens.com>
Signed-off-by: malc <av1474@comtv.ru>