system-arm: Enabled HDLcd by default in DTS

system-arm: Enabled HDLcd by default in DTS

This is fine as people using *_hdlcd.dtsi are willing to simulate
an HDLcd

JIRA: https://gem5.atlassian.net/browse/GEM5-866

Change-Id: Ifd5d6ecc81de920dbc29a05b07f30c13dcee3aa4
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/38797
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>
Tested-by: kokoro <noreply+kokoro@google.com>