Instead of having a generic "virt_qemu" board use "virt_qemu_<arch>" in
order to have a clean distinction between boards. Current supported
boards are "virt_qemu_arm_v7a", "virt_qemu_arm_v8a", and
"virt_qemu_riscv".
issue #4034
Always instantiating a network device with id `net0`, removes the need to call
append_qemu_nic_args in run scripts unless we want to add forwarding
rules.
genodelabs/genode#4311
Allow specifying additional qemu arguments for externally supported boards
(e.g. zynq_qemu) by adding a `qemu_args` file in the board-property directory.
The syntax of the qemu_args file is as follows:
- Arguments can appear in a single line or in multiple lines as the
lines will be appended (separated by a whitespace) to the global
qemu_args variable.
- If the line is prepended with a `foobar:` expression. The arguments
are only added if the foobar spec is present.
Note, that a `-m` argument specified in the qemu_args file will
override the arguments provided by the run scripts.
genodelabs/genode#4311
