pmdomain: imx8mp-blk-ctrl: Keep gpc power domain on for system wakeup

pmdomain: imx8mp-blk-ctrl: Keep gpc power domain on for system wakeup

Current design will power off all dependent GPC power domains in
imx8mp_blk_ctrl_suspend(), even though the user device has enabled
wakeup capability. The result is that wakeup function never works
for such device.

An example will be USB wakeup on i.MX8MP. PHY device '382f0040.usb-phy'
is attached to power domain 'hsioblk-usb-phy2' which is spawned by hsio
block control. A virtual power domain device 'genpd:3:32f10000.blk-ctrl'
is created to build connection with 'hsioblk-usb-phy2' and it depends on
GPC power domain 'usb-otg2'. If device '382f0040.usb-phy' enable wakeup,
only power domain 'hsioblk-usb-phy2' keeps on during system suspend,
power domain 'usb-otg2' is off all the time. So the wakeup event can't
happen.

In order to further establish a connection between the power domains
related to GPC and block control during system suspend, register a genpd
power on/off notifier for the power_dev. This allows us to prevent the GPC
power domain from being powered off, in case the block control power
domain is kept on to serve system wakeup.

Suggested-by: Ulf Hansson <ulf.hansson@linaro.org>
Fixes: 556f5cf9568a ("soc: imx: add i.MX8MP HSIO blk-ctrl")
Cc: stable@vger.kernel.org
Signed-off-by: Xu Yang <xu.yang_2@nxp.com>
Signed-off-by: Ulf Hansson <ulf.hansson@linaro.org>