OMAP2/3 clkdm/pwrdm: move wkdep/sleepdep handling from pwrdm to clkdm

Move clockdomain wakeup dependency and sleep dependency data
structures from the powerdomain layer to the clockdomain layer, where
they belong.  These dependencies were originally placed in the
powerdomain layer due to unclear documentation; however, it is clear
now that these dependencies are between clockdomains.  For OMAP2/3,
this is not such a big problem, but for OMAP4 this needs to be fixed.

Thanks to Benoît Cousson <b-cousson@ti.com> for his advice on this
patch.

Signed-off-by: Paul Walmsley <paul@pwsan.com>
Cc: Benoît Cousson <b-cousson@ti.com>