s390x/css: Introduce an ESW struct

s390x/css: Introduce an ESW struct

The Interrupt Response Block is comprised of several other
structures concatenated together, but only the 12-byte
Subchannel-Status Word (SCSW) is defined as a proper struct.
Everything else is a simple array of 32-bit words.

Let's define a proper struct for the 20-byte Extended-Status
Word (ESW) so that we can make good decisions about the sense
data that would go into the ECW area for virtual vs
passthrough devices.

[CH: adapted ESW definition to build with mingw, as discussed]
Signed-off-by: Eric Farman <[email protected]>
Message-Id: <20210617232537.1337506[email protected]>
Signed-off-by: Cornelia Huck <[email protected]>