cpu: Made TAGE a SimObject that can be used by other predictors

The TAGE implementation is now a SimObject so that other branch predictors
can easily use it. It has also been updated with the latest available TAGE
implementation from Andre Seznec:

http://www.irisa.fr/alf/downloads/seznec/TAGE-GSC-IMLI.tar

Change-Id: I2251b8b2d7f94124f9955f52b917dc3b064f090e
Reviewed-on: https://gem5-review.googlesource.com/c/15317
Reviewed-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>