Split internal and external sdcards

Two new types are introduced:
sdcard_internal
sdcard_external

The existing type of sdcard, is dropped and a new attribute
sdcard_type is introduced.

The boolean app_sdcard_rw has also been changed to allow for
controlling untrusted_app domain to use the internal and external
sdcards.

Change-Id: Ic7252a8e1703a43cb496413809d01cc6cacba8f5
diff --git a/attributes b/attributes
index ef4a170..7d491e2 100644
--- a/attributes
+++ b/attributes
@@ -24,6 +24,9 @@
 # All types use for sysfs files.
 attribute sysfs_type;
 
+# Attribute used for all sdcards
+attribute sdcard_type;
+
 # All types used for nodes/hosts.
 attribute node_type;