ARM: davinci: da8xx: move usb code to new file

We will be adding more da8xx-specific code for phy and clocks, so it will
be better to have this in a separate file. This way we don't have a bunch
of #ifdefs for all of the da8xx stuff.

While at it, fix some checkpatch warnings coming from existing code.

Signed-off-by: David Lechner <david@lechnology.com>
[nsekhar@ti.com: typo and checkpatch fixes]
Signed-off-by: Sekhar Nori <nsekhar@ti.com>