ARM: davinci: dm646x: add new clock init using common clock framework

This adds the new board-specific clock init in mach-davinci/dm646x.c
using the new common clock framework drivers.

The #ifdefs are needed to prevent compile errors until the entire
ARCH_DAVINCI is converted.

Also clean up the #includes since we are adding some here.

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