Support ATSC license installation

[ Merge of http://go/wvgerrit/163900/ ]

ATSC licenses can be saved by calling
MediaDrm#setPropertyString("storeAtscLicense",<value>)
where <value> is
"<atsc-key-set-ID>:<license-file-data in Base64 format>"

Before storing an ATSC license a session must be opened and the
ATSC mode must be enabled.

Use MediaDrm#setPropertyString("atscMode","enable");

Bug: 176871821
Test: WV Unit/integration/Luci tests
Test: libwvdrmdrmplugin_hal_test
Test: GtsMediaTestCases
Change-Id: Iec2a8b7f87b1122395d06856202278b92316fdfe

libwvdrmengine/cdm/core/include/device_files.h

@@ -155,6 +155,9 @@ class DeviceFiles {
   virtual bool RetrieveLicense(const std::string& key_set_id,
                                CdmLicenseData* license_data,
                                ResponseType* result);
+  virtual ResponseType StoreAtscLicense(
+      const CdmKeySetId& key_set_id,
+      const std::string& serialized_license_data);
 
   virtual bool DeleteLicense(const std::string& key_set_id);
   virtual bool ListLicenses(std::vector<std::string>* key_set_ids);