Add support for TLP emulation

Add support for TLP emulation

This series adds support for Transaction Layer Packet (TLP) emulation
response gateway regions, enabling userspace device emulation software
to write TLP responses directly to lower layers without kernel driver
involvement.

Currently, the mlx5 driver exposes VirtIO emulation access regions via
the MLX5_IB_METHOD_VAR_OBJ_ALLOC ioctl. This series extends that
ioctl to also support allocating TLP response gateway channels for
PCI device emulation use cases.

Signed-off-by: Leon Romanovsky <leon@kernel.org>