This splits poll_table into one structure used by f_op->poll and one
structure used by the implemenation of sys_poll/sys_select: poll_table
contains just the callback function pointer.  struct poll_wrapper
additionally contains err and table, i.e.  the members used by the poll
implementation.

Changes:
- split poll_table into 2 structures
- reorder the declarations in <linux/poll.h> accordingly
- uninline poll_initwait().