Bluetooth: Controller: Fix HCI Reset Command implementation

Added implementation for HCI Reset Command. Implementation
gracefully disables any running advertiser, observer, and/
or connection roles, and it resets controller context members.
The HCI Reset Command is implemented in such a way that
driver instances shared with other sub-systems and
application is not disturbed and instance/references used
by Bluetooth Controller are gracefully returned back.

Jira: ZEP-1282

Change-id: Ifb9ae6807736b5ec2d9f346cf2a590322056bcee
Signed-off-by: Vinayak Chettimada <vinayak.kariappa.chettimada@nordicsemi.no>
Signed-off-by: Carles Cufi <carles.cufi@nordicsemi.no>