dev-arm, system-arm: Remove HDLcd from VExpress_GEM5_VX platforms

dev-arm, system-arm: Remove HDLcd from VExpress_GEM5_VX platforms

This is a major change in our platform configuration.
At the moment the VExpress_GEM5_V1 and VExpress_GEM5_V2 platforms
both instantiate an HDLcd device. As the presence of the device
can slow down host performances when the software stack is
aware of its presence, we have historically been providing
an entry in the hdlcd DTB node to "hide" the entry from the
DTB parser:

status = "disable";

This default entry in the hdlcd node will in fact prevent the driver
from bringing up the device. Unfortunately this is useful for
experienced users only which are aware of this knob.

In order to make things more transparent, and to avoid any confusion
(e.g. having the hdlcd present in the config.ini, but not being able to
program it in Linux) we are deprecating this solution; we are removing
the HDLcd from the aforementioned platforms.

Users not interested on simulating a display controller won't
notice the difference.
Users interested on including it, will now have to switch to a new

VExpress_GEM5_Vx_HLCD platform

which will enabled the HDLcd without any further tweaking required

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

Change-Id: I4b1920efe764080115a57f52d8a3df2e6e2386a0
Signed-off-by: Giacomo Travaglini <giacomo.travaglini@arm.com>
Reviewed-on: https://gem5-review.googlesource.com/c/public/gem5/+/38796
Tested-by: kokoro <noreply+kokoro@google.com>
Reviewed-by: Andreas Sandberg <andreas.sandberg@arm.com>
Maintainer: Andreas Sandberg <andreas.sandberg@arm.com>