Split the OMAP1 and OMAP2+ platform_device build and register code.
Convert the OMAP2+ variant to use omap_device.

This patch was developed in collaboration with Rajendra Nayak
<rnayak@ti.com>.
Signed-off-by: NPaul Walmsley <paul@pwsan.com>
Signed-off-by: NRajendra Nayak <rnayak@ti.com>
Cc: Kevin Hilman <khilman@deeprootsystems.com>
Signed-off-by: NKevin Hilman <khilman@deeprootsystems.com>