mdadm: use struct context in reshape_super()

mdadm: use struct context in reshape_super()

reshape_super() takes too many arguments. Change passing params in
favor of single struct.

Add devname pointer and change direction members to struct shape
and use it for reshape_super().

Create reshape_array_size() and reshape_array_non_size() to handle
reshape_super() calls.

Signed-off-by: Mateusz Kusiak <mateusz.kusiak@intel.com>
Signed-off-by: Mariusz Tkaczyk <mariusz.tkaczyk@linux.intel.com>