fstrim: cleanup usage()

Signed-off-by: Karel Zak <kzak@redhat.com>
libmount: add efivarfs to the list of pseudo filesystems

Signed-off-by: Karel Zak <kzak@redhat.com>
fstrim: add --all to discard all filesystem

 * read /proc/self/mountinfo to get filesystems
 * ignore net and pseudo filesystems
 * ignore unaccessible filesystems (over mounted by another FS)
 * read disk sysfs queue/discard_granularity to detect is discard support
 * call FITRIM ioctl
 * silently ignore EOPNOTSUPP (for example LUKS without discard) and ENOTTY
   (for example vfat) errors

Signed-off-by: Karel Zak <kzak@redhat.com>