ARM: OMAP2+: Drop legacy platform data for dra7 mcasp

With recent ti-sysc driver changes, we can probe most devices with device
tree data only and drop the custom "ti,hwmods" property.

Let's drop the legacy platform data and custom "ti,hwmods" property. We
want to do this in a single patch as the "ti,hwmods" property is used to
allocate platform data dynamically that we no longer want to do.

Cc: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tony Lindgren <tony@atomide.com>