davinci: move PSC register definitions from psc.c to psc.h

The motivation behind the change is to use the same
definitions in the assembly code responsible for
suspending the SoC, a part of which is to clock gate
the DDR2 clock.

Note that the assembly code cannot invoke the C function
meant for this. The main reason being that stack in DDR2
cannot be accessed while DDR2 clock is being clock gated.

Signed-off-by: Sekhar Nori <nsekhar@ti.com>
Signed-off-by: Kevin Hilman <khilman@deeprootsystems.com>