IB/core: Introduce signature verbs API

Introduce a verbs interface for signature-related operations.  A
signature handover operation configures the layouts of data and
protection attributes both in memory and wire domains.

Signature operations are:

- INSERT:
  Generate and insert protection information when handing over
  data from input space to output space.
- validate and STRIP:
  Validate protection information and remove it when handing over
  data from input space to output space.
- validate and PASS:
  Validate protection information and pass it when handing over
  data from input space to output space.

Once the signature handover opration is done, the HCA will offload
data integrity generation/validation while performing the actual data
transfer.

Additions:

1. HCA signature capabilities in device attributes
    Verbs provider supporting signature handover operations fills
    relevant fields in device attributes structure returned by
    ib_query_device.

2. QP creation flag IB_QP_CREATE_SIGN...