Add back Keymaster hwservice context

keystore tries to find Keymaster and was being denied by SELinux leading
it to repeatedly reboot.

Test: manually boot microdroid and observe logcat
Bug: 192555229
Change-Id: If2b54fa5a3749ce5e449640925e360c8e44caf0d
diff --git a/microdroid/sepolicy/system/private/hwservice_contexts b/microdroid/sepolicy/system/private/hwservice_contexts
index f4583e2..9b47b06 100644
--- a/microdroid/sepolicy/system/private/hwservice_contexts
+++ b/microdroid/sepolicy/system/private/hwservice_contexts
@@ -1,3 +1,4 @@
+android.hardware.keymaster::IKeymasterDevice                    u:object_r:hal_keymaster_hwservice:s0
 android.hidl.allocator::IAllocator                              u:object_r:hidl_allocator_hwservice:s0
 android.hidl.base::IBase                                        u:object_r:hidl_base_hwservice:s0
 android.hidl.manager::IServiceManager                           u:object_r:hidl_manager_hwservice:s0