Add baknshot2_xip_vm_ops. Currently use a fake inode number.
Add test_mmap.c.

Currently we need:
1. A user space library in libnvm.
2. A inode number translation.
3. A file size update (perhaps).
test_mmap refine
bankshot2_new_inode
bankshot2_increase_inode_table_size
bankshot2_update_inode