Add platform/system/nvram to the manifest.

The platform/system/nvram repository contains the code for encoding
request and response messages to communicate with access-controlled
NVRAM HAL implementations, similar to what we have for gatekeeper and
keymaster.

BUG: 25762536

default.xml

@@ -509,6 +509,7 @@
   <project path="system/media" name="platform/system/media" groups="pdk" />
   <project path="system/nativepower" name="platform/system/nativepower" />
   <project path="system/netd" name="platform/system/netd" groups="pdk" />
+  <project path="system/nvram" name="platform/system/nvram" />
   <project path="system/security" name="platform/system/security" groups="pdk" />
   <project path="system/tools/aidl" name="platform/system/tools/aidl" groups="pdk-cw-fs,pdk-fs" />
   <project path="system/tpm" name="platform/system/tpm" />