ASoC: dapm: Add platform stream event support

Currently stream events are only perfomed on codec stream widgets only.
There is now a need to be able to perform stream events on platform
widgets too.

e.g. we have the ABE platform driver with several DAI links
to dummy codecs. We need to be able to perform stream events on any
of the dummy codec DAI links.

This patch also removes the snd_soc_dai * parameter since it's already
contained within the rtd * parameter.

Finally makle stream event return void since no one checks it anyway.

Signed-off-by: Liam Girdwood <lrg@ti.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>