GFX: optimize vmalloc allocation as it's fragmented severely byPVR driver

GFX: optimize vmalloc allocation as it's fragmented severely byPVR driver

BZ: 31145

GFX allocates lots of 1 page szie vmalloc areas. It causes dramatic
vmalloc fragmentation. Most such small vmalloc areas are created
as PVRSRV_HAP_WRITECOMBINE. We create a special gen_pool based on
a big vmalloc area. Then, allocate all small PVRSRV_HAP_WRITECOMBINE
request from the pool.

Change-Id: Ia38c4cc78e0e716a52cbd3592b2f8bcf099e08c8
Signed-off-by: Yanmin Zhang <yanmin.zhang@intel.com>
Signed-off-by: chenlinz <linx.z.chen@intel.com>
Reviewed-on: http://android.intel.com:8080/46647
Reviewed-by: Jiang, Fei <fei.jiang@intel.com>
Reviewed-by: Tu, Yun <yun.tu@intel.com>
Reviewed-by: Zeng, Li <li.zeng@intel.com>
Reviewed-by: Tong, BoX <box.tong@intel.com>
Tested-by: Tong, BoX <box.tong@intel.com>
Reviewed-by: buildbot <buildbot@intel.com>
Tested-by: buildbot <buildbot@intel.com>