ibmvscsi: Remove unsupported host config MAD

A VIOSRP_HOST_CONFIG_TYPE management datagram (MAD) has existed in the
code for some time. From what information I've gathered from Brian King
this was likely implemented on the host side in a SLES 9 based VIOS,
which is no longer supported anywhere. Further, it is not defined in
PAPR or supported by any AIX based VIOS.

Treating as bit rot and removing the associated host config code.  The
config attribute and its show function are left as not to break
userspace. The behavior remains the same returning nothing.

Signed-off-by: Tyrel Datwyler <tyreld@linux.vnet.ibm.com>
Reviewed-by: Johannes Thumshirn <jthumshirn@suse.de>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>