decouple HCE from FEATURE_NFC

Allows getting an instance of NfcAdapter through
NfcAdapter.getNfcAdapter on a device which has
FEATURE_NFC_HOST_CARD_EMULATION(_NFCF) but not FEATURE_NFC.

All non-HCE APIs will throw an UnsupportedOperationException if accessed
without FEATURE_NFC.

Bug: 24532713
Change-Id: I95c0309d8eea46f592b3c713541a3ed6e0f96aef