soc: imx: imx8mp-blk-ctrl: register HSIO PLL clock as bus_power_dev child

The blk-ctrl device is deliberately placed outside of the GPC power
domain as it needs to control the power sequencing of the blk-ctrl
domains together with the GPC domains.

Clock runtime PM works by operating on the clock parent device, which
doesn't translate into the neccessary GPC power domain action if the
clk parent is not part of the GPC power domain. Use the bus_power_device
as the parent for the clock to trigger the proper GPC domain actions on
clock runtime power management.

Fixes: 2cbee26e

 ("soc: imx: imx8mp-blk-ctrl: expose high performance PLL clock")
Reported-by: Yannic Moog <Y.Moog@phytec.de>
Signed-off-by: Lucas Stach <l.stach@pengutronix.de>
Tested-by: Yannic Moog <y.moog@phytec.de>
Signed-off-by: Shawn Guo <shawnguo@kernel.org>