OMAP: mcbsp: Move core driver under sound/soc/omap

In order to consolidate the McBSP driver move it out from
arch/arm/plat-omap directory under sound/soc/omap/

Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Acked-by: Tony Lindgren <tony@atomide.com>
Tested-by: Grazvydas Ignotas <notasas@gmail.com>
Tested-by: Janusz Krzysztofik <jkrzyszt@tis.icnet.pl>
Acked-by: Jarkko Nikula <jarkko.nikula@bitmer.com>
Signed-off-by: Liam Girdwood <lrg@ti.com>