test/qtest: add riscv-iommu-pci tests

test/qtest: add riscv-iommu-pci tests

To test the RISC-V IOMMU emulation we'll use its PCI representation.
Create a new 'riscv-iommu-pci' libqos device that will be present with
CONFIG_RISCV_IOMMU.  This config is only available for RISC-V, so this
device will only be consumed by the RISC-V libqos machine.

Start with basic tests: a PCI sanity check and a reset state register
test. The reset test was taken from the RISC-V IOMMU spec chapter 5.2,
"Reset behavior".

More tests will be added later.

Signed-off-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Reviewed-by: Frank Chang <frank.chang@sifive.com>
Acked-by: Alistair Francis <alistair.francis@wdc.com>
Message-ID: <20241016204038.649340-8-dbarboza@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>