There was no block transfer code in pm_smbus.c, and it is needed
for some devices.  So add it.

This adds both byte-by-byte block transfers and buffered block
transfers.

Signed-off-by: Corey Minyard <cminyard@mvista.com>
Cc: Michael S. Tsirkin <mst@redhat.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <1534796770-10295-5-git-send-email-minyard@acm.org>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>