davinci: make it possible to include clock.h and psc.h in assembly code

psc.h contains register defines for PSC module which
need to be accessed in assembly code which helps the
DA850/OMAP-L138 SoC go to sleep. Shutting down DDR clock
using PSC is a part of the sleep procedure.

Also, the PLL related hardware definitions in clock.h are
needed in assembly code to bypass the DDR2 PLL.

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