Adds default keymaster service to the early_hal class

The keymaster service is required by vold which starts very early
during boot up. This leads to the dependency loop:
init->installkey->vdc->vold->keymaster-service->init

This patch resolves this issue by adding service keymaster to the class
early-hal which will get started right after hwservicemanager on devices
that get treble.

Bug: 35764921
Test: Device boots. And lshal shows that service keymaster has two
      clients, keystore and vold.

Change-Id: Id0b6722de900b5513d46adb81d76b02fa6e155df