Provide *_init functions that populate an I2CAdapter struct without
allocating one, and make the existing *_create functions wrap them.
Because in the new setup *_create might return a pointer inside the
IMXI2C or OMAPI2C struct, create companion *_free functions to go
back to the outer pointer.
All this is temporary until allocation will be handled entirely by
qgraph.
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
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