ASoC: Fix wrong include for McPDM

McPDM needs platt/cpu.h for omap_rev and not omap_hwmod.h.
Drivers must not include omap_hwmod.h at, it will be
private to mach-omap2 soon. Fix the problem before other
drivers will also start including omap_hwmod.h.

Note that also plat/cpu.h will be going away, so the
omap_rev check needs to be replaced with mcpdm-watchdog
flag from platform_data or DT.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>