Adding a constant for /metadata/gsi/dsu/avb/.

Adding a constant to preserve DSU AVB keys from the ramdisk to
/metadata/gsi/dsu/avb/. This can be used for DSU installation service
to see if any matching key is found in the ramdisk at image installation
time.

Bug: 146910547
Test: boot device, checks the avb keys are copied to /metadata/gsi/dsu/avb/.
Change-Id: Idc88436bd074a273a7e09e589e4fd64a0580ff7e
1 file changed