attestation: Rename "chromeos" -> "brillo" in include paths and namespaces

libchromeos is transitioning to libbrillo and chromeos namespaces
and include directory is changing to brillo.

Bug: 24872993
TEST=built for aosp and brillo, all unit tests pass on dragonboard

Change-Id: I3d7f1eb480f9e211606d7ee0a990c4a1bec27ea8
1 file changed