Move timers dump/restore code into separate file

[xemul]

trafficstars

In criu/cr-restore.c file there's a set of functions starting from prepare_posix_timers() and prepare_itimers(). In criu/parasite-syscall.c there's a set starting from parasite_dump_itimers_seized() and parasite_dump_posix_timers_seized().

Both are better to be moved to separate .c file in the criu/ directory.

[Rajiv2605]

@adrianreber This issue seems unresolved/ open. Can I work on this issue?

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