System_Property_Get: Allow specifying multiple prop file paths

Some OEMs include prop files in custom locations. Add these to
a list and parse when setting properties.

Use the flag TW_SYSTEM_BUILD_PROP_ADDITIONAL_PATHS followed
by a semi-colon-separated list of paths (relative to /system)
where the additional prop files can be found.

The standard build.prop file does not need to be specified and
will always be parsed.

Example:
TW_SYSTEM_BUILD_PROP_ADDITIONAL_PATHS := etc/buildinfo/oem_build.prop;etc/prop.default

Change-Id: Ie0e25c7d2575d928310ff1b4fc1aef44a83784ca
diff --git a/twrp-functions.hpp b/twrp-functions.hpp
index e61038e..b04447b 100755
--- a/twrp-functions.hpp
+++ b/twrp-functions.hpp
@@ -101,7 +101,7 @@
 	static int write_to_file(const string& fn, const string& line);             //write to file
 	static bool Try_Decrypting_Backup(string Restore_Path, string Password); // true for success, false for failed to decrypt
 	static string System_Property_Get(string Prop_Name);                // Returns value of Prop_Name from reading /system/build.prop
-	static string System_Property_Get(string Prop_Name, TWPartitionManager &PartitionManager, string Mount_Point);                // Returns value of Prop_Name from reading /system/build.prop
+	static string System_Property_Get(string Prop_Name, TWPartitionManager &PartitionManager, string Mount_Point, string prop_file_name);     // Returns value of Prop_Name from reading provided prop file
 	static string Get_Current_Date(void);                               // Returns the current date in ccyy-m-dd--hh-nn-ss format
 	static void Auto_Generate_Backup_Name();                            // Populates TW_BACKUP_NAME with a backup name based on current date and ro.build.display.id from /system/build.prop
 	static void Fixup_Time_On_Boot(const string& time_paths = ""); // Fixes time on devices which need it (time_paths is a space separated list of paths to check for ats_* files)