clk: qcom: mmcc8974: Use gdscs .parent and remove genpd calls

With gdsc driver capable of handling hierarchical power domains,
specify oxili_gdsc as parent of oxilicx_gdsc.

Remove all direct calls to genpd from the mmcc clock driver. The
adding and removing of subdomains is now handled from within
the gdsc driver.

Signed-off-by: Rajendra Nayak <rnayak@codeaurora.org>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>