qup-i2c devices on sc7180 are clocked with a fixed clock (19.2 MHz)
Though qup-i2c does not support DVFS, it still needs to vote for a
performance state on 'CX' to satisfy the 19.2 Mhz clock frequency
requirement.

Use 'required-opps' to pass this information from
device tree, and also add the power-domains property to specify
the CX power-domain.
Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Ulf Hansson <ulf.hansson@linaro.org>
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>