Linux 4.14 compat: IO acct, global_page_state, etc (#6655)

Linux 4.14 compat: IO acct, global_page_state, etc (#6655)

generic_start_io_acct/generic_end_io_acct in the master
branch of the linux kernel requires that the request_queue
be provided.

Move the logic from freemem in the spl to arc_free_memory
in arc.c. Do this so we can take advantage of global_page_state
interface checks in zfs.

Upstream kernel replaced struct block_device with
struct gendisk in struct bio. Determine if the
function bio_set_dev exists during configure
and have zfs use that if it exists.

bio_set_dev https://github.com/torvalds/linux/commit/74d4699
global_node_page_state https://github.com/torvalds/linux/commit/75ef718
io acct https://github.com/torvalds/linux/commit/d62e26b

Reviewed-by: Brian Behlendorf <behlendorf1@llnl.gov>
Signed-off-by: Giuseppe Di Natale <dinatale2@llnl.gov>
Closes #6635

Signed-off-by: Brian Behlendorf <behlendorf1@llnl.gov>