habanalabs: add uapi to flush inbound HBM transactions

When doing p2p with a NIC device, the NIC needs to make sure all the
writes to the HBM (through the PCI bar of the Gaudi device) were
flushed.

It can be done by either the NIC or the host reading through the PCI
bar.

To support the host side, we supply a simple uapi to perform this flush
through the driver, because the user can't create such a transaction
by itself (the PCI bar isn't exposed to normal users).

Signed-off-by: Ohad Sharabi <osharabi@habana.ai>
Reviewed-by: Oded Gabbay <ogabbay@kernel.org>
Signed-off-by: Oded Gabbay <ogabbay@kernel.org>

habanalabs: move driver to accel subsystem

Now that we have a subsystem for compute accelerators, move the
habanalabs driver to it.

This patch only moves the files and fixes the Makefiles. Future
patches will change the existing code to register to the accel
subsystem and expose the accel device char files instead of the
habanalabs device char files.

Update the MAINTAINERS file to reflect this change.

Signed-off-by: Oded Gabbay <ogabbay@kernel.org>