powerpc/64s/pgtable: Enable directMap counters in meminfo for Hash

powerpc/64s/pgtable: Enable directMap counters in meminfo for Hash

This patch enables the directMap counters to be printed in proc/meminfo
for Hash mmu. With this patch on a system with 8G of DRAM we can see the
entire RAM mapped with 16M pagesize:

cat /proc/meminfo |grep -i direct
DirectMap4k:           0 kB
DirectMap64k:          0 kB
DirectMap16M:    8388608 kB
DirectMap16G:          0 kB

Tested with devdax too:
root@buildroot:/# ndctl create-namespace -r region0 -m devdax -s 2G
{
  "dev":"namespace0.0",
  "mode":"devdax",
  "map":"dev",
  "size":"2032.00 MiB (2130.71 MB)",
  "uuid":"aa383ded-cd99-43a0-979f-5225467cfb40",
  "daxregion":{
    "id":0,
    "size":"2032.00 MiB (2130.71 MB)",
    "align":16777216,
    "devices":[
      {
        "chardev":"dax0.0",
        "size":"2032.00 MiB (2130.71 MB)",
        "target_node":0,
        "align":"16.00 MiB (16.78 MB)",
        "mode":"devdax"
      }
    ]
  },
  "align":16777216
}
root@buildroot:/# cat /proc/meminfo |grep -i direct
DirectMap4k:           0 kB
DirectMap64k:          0 kB
DirectMap16M:   10485760 kB
DirectMap16G:          0 kB

root@buildroot:/# ndctl destroy-namespace -f all
destroyed 1 namespace
root@buildroot:/# cat /proc/meminfo |grep -i direct
DirectMap4k:           0 kB
DirectMap64k:          0 kB
DirectMap16M:    8388608 kB
DirectMap16G:          0 kB

Signed-off-by: Ritesh Harjani (IBM) <ritesh.list@gmail.com>
Signed-off-by: Madhavan Srinivasan <maddy@linux.ibm.com>
Link: https://patch.msgid.link/ffe47912e17075649b6ce5b2ee5d7f3eb5352e0b.1761834163.git.ritesh.list@gmail.com