[CRIU] Fix compilation on ARM

[Alexander Kartashov]

Dear colleagues,

This patchset fixes compilation on ARM caused by the patchset
"rain user memory from task before dumping". This patchset

* Fixes the ARM parasite head dropping manual tuning of the symbol
  offsets.
* Adds the description of the system call vmsplice().

Unfortunately, the test static/maps04 fails on ARM: the test program
is checkpointed/restored successfully but the test hangs then
and killed on a timeout.

--
Sincerely yours,
Alexander Kartashov