vm/qemu: add {{TCP_PORT}} for configs
vm/qemu: add {{TCP_PORT}} for configs

This allows adding a free port to the custom QEMU command line.
One example is a gdb server built into QEMU.

Signed-off-by: Alexey Kardashevskiy <ac1fc56530d7d037e1ea666f130daca22d72f964@linux.ibm.com>

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