davinci: move PLL wait time values to clock.h

As suspend support is added, the code supporting
the suspend operation needs to bypass PLLs and
needs to access the same wait time values as the
PLL code in clock.c.

To facilitate this, move the PLL wait times to
clock.h where they can be accessed by suspend code.

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