PM: freezer: Rewrite restarting tasks log to remove stray *done.*

PM: freezer: Rewrite restarting tasks log to remove stray *done.*

`pr_cont()` unfortunately does not work here, as other parts of the
Linux kernel log between the two log lines:

    [18445.295056] r8152-cfgselector 4-1.1.3: USB disconnect, device number 5
    [18445.295112] OOM killer enabled.
    [18445.295115] Restarting tasks ...
    [18445.295185] usb 3-1: USB disconnect, device number 2
    [18445.295193] usb 3-1.1: USB disconnect, device number 3
    [18445.296262] usb 3-1.5: USB disconnect, device number 4
    [18445.297017] done.
    [18445.297029] random: crng reseeded on system resumption

`pr_cont()` also uses the default log level, normally warning, if the
corresponding log line is interrupted.

Therefore, replace the `pr_cont()`, and explicitly log it as a separate
line with log level info:

    Restarting tasks: Starting
    […]
    Restarting tasks: Done

Signed-off-by: Paul Menzel <pmenzel@molgen.mpg.de>
Link: https://patch.msgid.link/20250511174648.950430-1-pmenzel@molgen.mpg.de
[ rjw: Rebase on top of an earlier analogous change ]
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>