ARM: davinci: Move clock init after ioremap.

Some clocks (such as the USB PHY clocks in DA8xx) will need to use iomem.
The davinci_common_init() function must be called before the ioremap, so
the clock init is now split out as separate function.

Signed-off-by: David Lechner <david@lechnology.com>
Signed-off-by: Sekhar Nori <nsekhar@ti.com>