ehci-omap: Clean up added ehci-omap.c

Clean up added ehci-omap.c and make it generic for re-use across
omap-soc having same ehci ip block. Also pass the modes to be configured
from board file and configure the ports accordingly. All usb layers
are not cache aligned, till then keep cache off for usb ops as ehci will use
internally dma for all usb ops.

* Add a generic common header ehci-omap.h having common ip block
  data and reg shifts.
* Rename and modify ehci-omap3 to ehci.h retain only conflicting
  sysc reg shifts remove others and move to common header file.
* pass the board data for beagle/panda accordinly to use
  ehci ports.

Acked-by: Igor Grinberg <grinberg@compulab.co.il>
Signed-off-by: Govindraj.R <govindraj.raja@ti.com>