Staging: lustre: obdclass: cl_io: Declare as static

Declare cl_page_list_assume, cl_io_cancel, cl_io_rw_advance,
cl_page_list_del, cl_page_list_discard, cl_page_list_fini as
static since they are used only in this particular file.
Also remove them from corresponding header files

Signed-off-by: Shraddha Barke <shraddha.6596@gmail.com>
Reviewed-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>