Add APIs to manage WriteBooster buffer

Five new APIs are introduced to manage and flush
UFS WriteBooster buffer.

Bug: 349648148
Test: StorageManager.*WriteBooster*
Change-Id: I2f82a2d8b08d83a63cbc3da4d9512792b0d472ba
Signed-off-by: Daniel Lee <chullee@google.com>
diff --git a/VoldUtil.h b/VoldUtil.h
index ce6b411..9fb9e96 100644
--- a/VoldUtil.h
+++ b/VoldUtil.h
@@ -21,3 +21,5 @@
 extern android::fs_mgr::Fstab fstab_default;
 
 #define DATA_MNT_POINT "/data"
+
+std::string GetUfsHostControllerSysfsPath();