Since the PM clock management code in drivers/base/power/clock_ops.c
is used for both runtime PM and system suspend/hibernation, the
definitions of data structures and headers related to it should not
be located in include/linux/pm_rumtime.h.  Move them to a separate
header file.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>

Since the power.subsys_data device field will be used by multiple
filesystems, introduce a reference counting mechanism for it to avoid
freeing it prematurely or changing its value at a wrong time.

Make the PM clocks management code that currently is the only user of
power.subsys_data use the new reference counting.
Signed-off-by: NRafael J. Wysocki <rjw@sisk.pl>