add DirectMap1G to meminfo

ISSUE:
```
2014/06/19 09:51:11 ignoring unknown meminfo field DirectMap1G
```
would like to add DirectMap1G to meminfo
```
# plu@plu-9: grep DirectMap /proc/meminfo 
DirectMap4k:      163988 kB
DirectMap2M:     7100416 kB
DirectMap1G:    26214400 kB
```