Add support for running Microdroid VM in run_microdroid_demo.sh

This change enables the script to run the Microdroid VM itself along with
the TC demo app. Use 'start-microdroid' to start the VM with an empty payload
and 'run-tc-app' to run the TC Microdroid demo app.

Signed-off-by: Ahmed Genidi <ahmed.genidi@arm.com>