Make HID Device service independent from HID Host.

By default, enabling the HID Device service is only possible
during disabling the HID Host service. If, on the other hand,
the HID Host service was never initialized, then a request to
enable the HID Device service should just be executed
immediately.

Test: manual, on a device without the HID Host profile.
Change-Id: I2ab4b8aec413b66d57eb322d38660f1b4c48ba32