fscrypt: Wrapped key support for FBE

Commit imported from:

https: //github.com/LineageOS/android_system_vold/commit/ce024f07c23d0649635a336fff389332b9806f48
Change-Id: I924a9fcbac7d790609fbafcf8c12654fdb267e32
diff --git a/crypto/fscrypt/Keymaster.h b/crypto/fscrypt/Keymaster.h
index 42a2b5d..4301a9c 100644
--- a/crypto/fscrypt/Keymaster.h
+++ b/crypto/fscrypt/Keymaster.h
@@ -102,6 +102,9 @@
     explicit operator bool() { return mDevice.get() != nullptr; }
     // Generate a key in the keymaster from the given params.
     bool generateKey(const km::AuthorizationSet& inParams, std::string* key);
+	// Export a key from keymaster.
+    bool exportKey(km::KeyFormat format, KeyBuffer& kmKey, const std::string& clientId,
+                   const std::string& appData, std::string* key);
     // If the keymaster supports it, permanently delete a key.
     bool deleteKey(const std::string& key);
     // Replace stored key blob in response to KM_ERROR_KEY_REQUIRES_UPGRADE.