Bluetooth: HID: Add support for Set Idle and Get Idle Commands (3/4)

This patch provides an interface for application to send Set Idle
and Get Idle commands to remote HID Device. Support for these
two commands was missing from exisitng code, so existing code
design is reused to add support for these two commands.

Without this support following mandatory PTS test cases for HID 1.0
cannot be passed, TC_HOS_HID_BV_05/06.

Change-Id: I548362cc328498920b2dae740f1a76b2cc2d6a67
CRs-Fixed: 522511