read partition length from recovery.fstab

Don't hardcode magical partition behavior in the script generator.

Change-Id: I4aeea022f8a32a7c9f316be2c2514510344ca0e0
diff --git a/tools/releasetools/edify_generator.py b/tools/releasetools/edify_generator.py
index 4ed1a07..893cb45 100644
--- a/tools/releasetools/edify_generator.py
+++ b/tools/releasetools/edify_generator.py
@@ -172,11 +172,9 @@
     fstab = self.info.get("fstab", None)
     if fstab:
       p = fstab[partition]
-      # Reserve the last 16 Kbytes of an EMMC /data for the crypto footer
-      if partition == "/data" and common.PARTITION_TYPES[p.fs_type] == "EMMC":
-        reserve_size = -16384
       self.script.append('format("%s", "%s", "%s", "%s");' %
-                         (p.fs_type, common.PARTITION_TYPES[p.fs_type], p.device, reserve_size))
+                         (p.fs_type, common.PARTITION_TYPES[p.fs_type],
+                          p.device, p.length))
     else:
       # older target-files without per-partition types
       partition = self.info.get("partition_path", "") + partition