hw/i386: Rename default_bus_bypass_iommu

hw/i386: Rename default_bus_bypass_iommu

Since commit d8fb7d0969d5 ("vl: switch -M parsing to keyval"), machine
parameter definitions cannot use underscores, because keyval_dashify()
transforms them to dashes and the parser doesn't find the parameter.

This affects option default_bus_bypass_iommu which was introduced in the
same release:

$ qemu-system-x86_64 -M q35,default_bus_bypass_iommu=on
qemu-system-x86_64: Property 'pc-q35-6.1-machine.default-bus-bypass-iommu' not found

Rename the parameter to "default-bus-bypass-iommu". Passing
"default_bus_bypass_iommu" is still valid since the underscore are
transformed automatically.

Fixes: c9e96b04fc19 ("hw/i386: Add a default_bus_bypass_iommu pc machine option")
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Tested-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Jean-Philippe Brucker <jean-philippe@linaro.org>
Message-Id: <20211025104737.1560274-1-jean-philippe@linaro.org>
Cc: qemu-stable@nongnu.org
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>