kdbus: porting to 4.14

kdbus: porting to 4.14

This commit makes kdbus driver working with kernel 4.14.
It also enabled compilation of the driver if enabled in config.

The list of changes needed to make it compile with kernel 4.14:
- Add missing includes for <linux/cred.h>
- put inode_lock()/inode_unlock() in place of explicit mutex locking
- replace CURRENT_TIME with proper call to current_time()
- replace PAGE_CACHE_* with PAGE_*
- replace GFP_TEMPORARY with GFP_KERNEL
- use kvecs for kernel memory, iovec for user memory instead of only iovec
  for both
- fix usage of task_cgroup_path()
- replace GROUP_AT usage with 'gid' field dereference
- add 0 as an argument to init_name_hash
- add 0 as flags as an argument to vfs_iter_write
- replace __vfs_read with kernel_read to allow compilation into module

Change-Id: I3dd066ab531d0d3f7082556e4d38381961998015
Signed-off-by: Adrian Szyndela <adrian.s@samsung.com>