lib: genalloc: Add API to allocate at specified addr.

Add API to allocate at specified alloc address.

Change-Id: I188e5430220c050026c6a3e17a586012d9a9fa04
Signed-off-by: Krishna Reddy <vdumpa@nvidia.com>
Reviewed-on: http://git-master/r/74468
Reviewed-by: Automatic_Commit_Validation_User
Reviewed-by: Stephen Warren <swarren@nvidia.com>