Securely encrypt the master key

Move all key management into vold
Reuse vold's existing key management through the crypto footer
to manage the device wide keys.

Use ro.crypto.type flag to determine crypto type, which prevents
any issues when running in block encrypted mode, as well as speeding
up boot in block or no encryption.

This is one of four changes to enable this functionality:
  https://android-review.googlesource.com/#/c/148586/
  https://android-review.googlesource.com/#/c/148604/
  https://android-review.googlesource.com/#/c/148606/
  https://android-review.googlesource.com/#/c/148607/

Bug: 18151196

Change-Id: I3c68691717a61b5e1df76423ca0c02baff0dab98
diff --git a/Android.mk b/Android.mk
index c913a1e..d4a178a 100644
--- a/Android.mk
+++ b/Android.mk
@@ -15,6 +15,7 @@
 	Devmapper.cpp \
 	ResponseCode.cpp \
 	CheckBattery.cpp \
+	Ext4Crypt.cpp \
 	VoldUtil.c \
 	fstrim.c \
 	cryptfs.c