sparc64: Trim page tables for 2G pages

sparc64: Trim page tables for 2G pages

Currently mapping a 2G page requires 256*1024 PTE entries.
This results in large amounts of RAM to be used just for
storing page tables. We now use 256 PMD entries to map a
2G page which is much more space efficient.

Orabug: 23109070

Signed-off-by: Nitin Gupta <nitin.m.gupta@oracle.com>
(cherry picked from commit d3c88b8f27645c14cbb220570e5945abb0989d19)
(cherry picked from commit 768096d7916fefc497f397b0675455a754ee8a5b)
Signed-off-by: Allen Pais <allen.pais@oracle.com>