restore: Parse self maps via bfd

When injecting the restorer blob criu parses /proc/self/maps
file to find out the hole for the blob itself. It happens
every time and the maps file for criu is now HUGE (~12k),
so it's much more efficient to use bfd for it rather than
glibc's fopen.

Signed-off-by: Pavel Emelyanov <xemul@virtuozzo.com>
Signed-off-by: Andrei Vagin <avagin@virtuozzo.com>