clk: at91: clk-sam9x60-pll: allow runtime changes for pll

Allow runtime frequency changes for PLLs registered with proper flags.
This is necessary for CPU PLL on SAMA7G5 which is used by DVFS.

Signed-off-by: Claudiu Beznea <claudiu.beznea@microchip.com>
Link: https://lore.kernel.org/r/1605800597-16720-7-git-send-email-claudiu.beznea@microchip.com


Signed-off-by: Stephen Boyd <sboyd@kernel.org>