It is not being used in hot paths and is obsoleted by I2C_SLAVE()
QOM cast macro. Clean it up using a scripted conversion, so that it
doesn't get used in new code.

Some of its callers were combining it with FROM_I2C_SLAVE() macro, which
is equally obsolete but needs to be replaced in a type-specific way.
Signed-off-by: NAndreas Färber <afaerber@suse.de>
Cc: Kuo-Jung Su <dantesu@faraday-tech.com>
Signed-off-by: NAnthony Liguori <aliguori@us.ibm.com>