[ALSA] Additional credits to soc-core

This patch adds copyright and credit for my good friend Richard Purdie
from OpenedHand for his help and code contribution throughout the
development of the core code. Many thanks Richard (I guess we overlooked
this in trying to get everything working well).
It also adds some extra comments wrt to DAI clock matching.

Signed-off-by: Liam Girdwood <lg@opensource.wolfsonmicro.com>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Jaroslav Kysela <perex@suse.cz>