Compel: use (rt)-vdso/vvar for timings in PIE blobs

[0x7f454c46]

In PIE blobs (parasite/restorer) we use timings for logs - check sbuf_log_init():

	/*
	 * Format:
	 *
	 * (time)pie: pid: string-itself
	 */

This is all done in that function with raw syscalls:

		sys_gettimeofday(&now, NULL);
		timediff(&start, &now);

If we omit calling raw syscalls and use vdso for the purpose of logging, that will eliminate as much as one-syscall-per-PIE-message. Getting time without switching to kernel will speed up C/R, keeping logs as informative as they were.

During restore (in the restorer blob) - we know the position of vvar/vdso pair and vdso-symtable.
So, it should be simple to use gettimeofday from vvar page, calling vdso-provided function.

On the dumping - it's a bit more complex. We have vdso-symtable parsed in criu, but yet don't know if seized task has the same vdso-symtable. So, as we'll parse the symtable afterward anyway for dumping needs, this could be done during parasite's initialization and then using gettimeofday from seized task.