clk: rockchip: add pclk_cpu to the list of rk3188 critical clocks

pclk_cpu needs to keep running because it is needed for devices like
the act8865 regulator but with the recent gpio clock handling this is
not always the case anymore. So add it to the list of critical clocks.

Signed-off-by: Michael Niewoehner <linux@mniewoehner.de>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>