usb: hid: rework idle report implementation

HID core implementation has support for Get/Set Idle requests and
on idle report processing. Basically it has little use.
Also, it has no users in the tree except samples/subsys/usb/hid,
which does not have it turned on.
There are several issues with the idle report implementation:
- Core calls hid_ops.on_idle callback with Report ID 0,
  but this ID is reserved and should not be used.
  Report descriptors do not use Report ID index zero.
- Calling hid_ops.on_idle with Report ID 0 cann only
  be turned off by calling SetIdle(Duration = 0, Report ID = 0),
  but not by SetIdle with Report ID not equal zero.
- GetIdle with Report Id not equal zero returns wrong
  value after SetIdle(Duration = n, Report ID = 0)
- It may happen that hid_ops.on_idle is called for
  different Report ID during one and the same SoF event.
  But there can be only one hid_int_ep_write() during a frame.

This patch fixes listed issues and revises Get/Set Idle request,
and hid_sof_handler() implementation.

Signed-off-by: Johann Fischer <johann.fischer@nordicsemi.no>