OMAP: UART: omap_device conversions, remove implicit 8520 assumptions

Major rework of OMAP UART init for omap_device conversion as well as
use with either 8250 driver or new omap-serial driver.

In preparation for a new omap-serial driver, remove 8250 assumptions
and dependencies from the serial core.

Convert UART core and PM support to use omap_device layer. Also add
support for both console on 8250 or omap-serial driver.

omap_device conversion:
- Convert clock API calls to omap_device calls
- Remove all static platform_data setup and configuration.  This is
  all done by the omap_device build phase.

Signed-off-by: Govindraj.R <govindraj.raja@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>