Add HIDL backend to keystore service

This CL adds variants of the public key retrieval and signing
routine which use the WiFi Keystore HIDL for the backend.
The Android.mk has been modified to build a second variant of
the library to expose this HIDL backend.  While here, add
guards to all headers.

Bug: 34603782
Test: Able to connect to wifi passpoint networks.
Change-Id: I444ef383e4d3fdabc10c3e44c1bae9747613c8cf
6 files changed
tree: 7c83ecb665d2f4a7a8946d2bf99e6e6b8221dbfe
  1. keystore/
  2. keystore-engine/
  3. softkeymaster/
  4. MODULE_LICENSE_APACHE2
  5. NOTICE