clk: Hi6220: enable stub clock driver for ARCH_HISI

In current kernel config 'CONFIG_STUB_CLK_HI6220' is disabled by
default, as result stub clock driver has not been registered and
CPUFreq driver cannot work.

This patch is to enable stub clock driver in config for ARCH_HISI.

Reported-by: Dietmar Eggemann <dietmar.eggemann@arm.com>
Signed-off-by: Leo Yan <leo.yan@linaro.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>