Adds 'sriov_configure' to enable/disable virtual functions (VFs).
Also Initializes VF<=>PF mailbox IRQs, register handlers for
processing these mailbox messages.

Admin function (AF) handles resource allocation and configuration for
PFs and their VFs. PFs request the AF directly, via mailboxes.
Unlike PFs, VFs cannot send a mailbox request directly. A VF sends
mailbox messages to its parent PF, with which it shares a mailbox
region. The PF then forwards these messages to the AF. After handling
the request, the AF sends a response back to the VF, through the PF.

This patch adds support for this 'VF <=> PF <=> AF' mailbox
communication.
Signed-off-by: Suheil Chandran <schandran@marvell.com>
Signed-off-by: Lukasz Bartosik <lbartosik@marvell.com>
Signed-off-by: Srujana Challa <schalla@marvell.com>
Signed-off-by: Herbert Xu <herbert@gondor.apana.org.au>