When setting the PLL rates, check that:

 - VCO is within range
 - PFD is within range
 - PLL is disabled when postdiv is changed
 - postdiv2 <= postdiv1
Reviewed-by: NAndrew Bresticker <abrestic@chromium.org>
Signed-off-by: NKevin Cernekee <cernekee@chromium.org>
Signed-off-by: NEzequiel Garcia <ezequiel.garcia@imgtec.com>
Signed-off-by: NStephen Boyd <sboyd@codeaurora.org>