Reserve space in super for dynamic partition metadata

The maximum size of all dynamic partition groups should not exceed
the super size - DAP metadata size. Today the configuration of
the device doesn't take the metadata into acount.

Since we recommend 4M to partners, reserve 4M here.

Bug: 183360400 
Bug: 182431975
Change-Id: Idd6d01db2594b4598c03aecbf931009fcf92a36c
Test: TH
1 file changed