usb, kcov: collect coverage from hub_event

usb, kcov: collect coverage from hub_event

Add kcov_remote_start()/kcov_remote_stop() annotations to the
hub_event() function, which is responsible for processing events on USB
buses, in particular events that happen during USB device enumeration.

Since hub_event() is run in a global background kernel thread (see
Documentation/dev-tools/kcov.rst for details), each USB bus gets a
unique global handle from the USB subsystem kcov handle range.  As the
result kcov can now be used to collect coverage from events that happen
on a particular USB bus.

[[email protected]: avoid patch conflicts to make life easier for Andrew]
Link: http://lkml.kernel.org/r/de4fe1c219db2d002d905dc1736e2a3bfa1db997.1572366574.git.andreyknvl@google.com
Signed-off-by: Andrey Konovalov <[email protected]>
Reviewed-by: Greg Kroah-Hartman <[email protected]>
Cc: Alan Stern <[email protected]>
Cc: Alexander Potapenko <[email protected]>
Cc: Anders Roxell <[email protected]>
Cc: Arnd Bergmann <[email protected]>
Cc: David Windsor <[email protected]>
Cc: Dmitry Vyukov <[email protected]>
Cc: Elena Reshetova <[email protected]>
Cc: Jason Wang <[email protected]>
Cc: Marco Elver <[email protected]>
Cc: "Michael S. Tsirkin" <[email protected]>
Cc: Steven Rostedt <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>