clk: iproc: Allow plls to do minor rate changes without reset

The iproc plls are capable of doing small rate changes without the
need for a full reset and re-lock procedure.  This feature will
allow for small tweaks to the PLL rate to occur smoothly.

Signed-off-by: Lori Hikichi <lori.hikichi@broadcom.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>