Introduce the clk_hw_set_parent() provider call to change parent of
a clock by using the clk_hw pointers.

This eases the clock reparenting from clock rate notifiers and
implementing DVFS with simpler code avoiding the boilerplates
functions as __clk_lookup(clk_hw_get_name()) then clk_set_parent().
Signed-off-by: NNeil Armstrong <narmstrong@baylibre.com>
Acked-by: NMartin Blumenstingl <martin.blumenstingl@googlemail.com>
Acked-by: NStephen Boyd <sboyd@kernel.org>
Signed-off-by: NJerome Brunet <jbrunet@baylibre.com>