mmu: procfs support

Add procfs_maps() function to core/mmu.cc that returns all the VMAs
formatted for Linux compatible "/proc/<pid>/maps" file.

This will be called by the procfs filesystem.

Limitations:

  * Shared mappings are not identified as such.
  * File-backed mmap offset, device, inode, and pathname are not
    reported.
  * Special region names such as [heap] and [stack] are not reported.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
proc filesystem

This patch adds a simple Linux compatible procfs filesystem.  It
currently implements a "/proc/self/maps" file which is looked up by
OpenJDK during startup.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>
vfs: mount procfs at boot

Add a '/proc' directory to OSv image and mount procfs on it.

Signed-off-by: Pekka Enberg <penberg@cloudius-systems.com>