fs_mgr: increase tmpfs size to accommodate bigger dex2oat data

During encryption and decryption, art is pumping out data via
dex2oat into the /data that is actually a tmpfs.
It currently needs ~195MB.
So we increase the tmpfs from 128MB to 256MB.

Bug: 15909689
Change-Id: I5d518a87d7b4eccf32fcd77f61980646ee8a3d35
Signed-off-by: JP Abgrall <jpa@google.com>