Revert "hw/riscv/virt.c: imsics DT: add '#msi-cells'"

Revert "hw/riscv/virt.c: imsics DT: add '#msi-cells'"

This reverts commit f42cdf2ea5b3a1dc369792d7acbf9cd3e5c90815.

Linux does not properly handle '#msi-cells=<0>' when searching for
MSI controllers for PCI devices which results in the devices being
unable to use MSIs. A patch for Linux has been sent[1] but until it,
or something like it, is merged and in distro kernels we should stop
adding the property. It's harmless to stop adding it since the
absence of the property and a value of zero for the property mean
the same thing according to the DT binding definition.

Link: https://lore.kernel.org/all/20240816124957.130017-2-ajones@ventanamicro.com/
Signed-off-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Daniel Henrique Barboza <dbarboza@ventanamicro.com>
Message-ID: <20240816160743.220374-5-ajones@ventanamicro.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>