Correct the McBSP2/4 ick mapping (they were 2->4 and 4->2).
Add missing mcbsp clock aliases.
Collect the McBSP clock definition in one location at the same time.

Fixes the following warning on boot:
[    0.307739] omap_hwmod: mcbsp2: _wait_target_ready failed: -16
[    0.307769] omap_hwmod: mcbsp2: cannot be enabled for reset (3)
Signed-off-by: Peter Ujfalusi <peter.ujfalusi@ti.com>
Signed-off-by: Tero Kristo <t-kristo@ti.com>