hw/nvme: Make max_ioqpairs and msix_qsize configurable in runtime

hw/nvme: Make max_ioqpairs and msix_qsize configurable in runtime

The NVMe device defines two properties: max_ioqpairs, msix_qsize. Having
them as constants is problematic for SR-IOV support.

SR-IOV introduces virtual resources (queues, interrupts) that can be
assigned to PF and its dependent VFs. Each device, following a reset,
should work with the configured number of queues. A single constant is
no longer sufficient to hold the whole state.

This patch tries to solve the problem by introducing additional
variables in NvmeCtrl’s state. The variables for, e.g., managing queues
are therefore organized as:
 - n->params.max_ioqpairs – no changes, constant set by the user
 - n->(mutable_state) – (not a part of this patch) user-configurable,
                        specifies number of queues available _after_
                        reset
 - n->conf_ioqpairs - (new) used in all the places instead of the ‘old’
                      n->params.max_ioqpairs; initialized in realize()
                      and updated during reset() to reflect user’s
                      changes to the mutable state

Since the number of available i/o queues and interrupts can change in
runtime, buffers for sq/cqs and the MSIX-related structures are
allocated big enough to handle the limits, to completely avoid the
complicated reallocation. A helper function (nvme_update_msixcap_ts)
updates the corresponding capability register, to signal configuration
changes.

Signed-off-by: Łukasz Gieryk <lukasz.gieryk@linux.intel.com>
Reviewed-by: Klaus Jensen <k.jensen@samsung.com>
Acked-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Klaus Jensen <k.jensen@samsung.com>