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: NRajendra Nayak <rnayak@codeaurora.org>
Signed-off-by: NStephen Boyd <sboyd@codeaurora.org>