Introduce enbale_hca and disable_hca commands to signify when the
driver starts or ceases to operate on the device.

In addition the driver will use boot and init pages count; boot pages
is required to allow firmware to complete boot commands and the other
to complete init hca.  Command interface revision is bumped to 4 to
enforce using supported firmware.

This patch breaks compatibility with old versions of firmware (< 4);
however, the first GA firmware we will publish will support version 4
so this should not be a problem.

Signed-off-by: Eli Cohen <eli@mellanox.com>
Signed-off-by: Roland Dreier <roland@purestorage.com>