cpu: MinorCPU not updating cycle counter value

cpu: MinorCPU not updating cycle counter value

By not updating the cycle counter value for every tick in the
MinorCPU meant that a read to the associated performance counter
was always returning 0.

For more info check the following email thread in gem5-users:

https://www.mail-archive.com/gem5-users@gem5.org/msg18742.html

Change-Id: Ibc033b536669cbb43d40c8a7c0659eb5565bdf93
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/38095
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Gabe Black <gabe.black@gmail.com>
Reviewed-by: Jason Lowe-Power <power.jg@gmail.com>
Maintainer: Jason Lowe-Power <power.jg@gmail.com>