greybus: gbuf: have caller set actual_length

A Greybus buffer has both a transfer_buffer_size field, which is the
size in bytes of the transfer buffer, and an actual_length field,
which is the number of bytes in that buffer that are actually
consumed.  The user of the buffer--and not the buffer allocation
method--should be setting the actual_length field.

Stop setting the actual length on the es1-ap-usb alloc_gbuf_data
method.  And *do* set it in gb_operation_create(), where we can
presume the operation being allocated will consume all the bytes
requested.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>
greybus: specify type when creating an operation

The type of an operation belongs in the operation header, which
shouldn't be touched by users of the interface.  So specify it
at operation creation time.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>
greybus: add a connection->private field

This will be used for driver-specific data for whatever drives the
other end of the connection.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>
greybus: define gb_connection_err()

Define a function that prints error information about a Greybus
connection in a standard format.  This adopts the convention that
[M:I:C] represents the "path" the connection represents--specifying
the module id, the interface number on that module, and the
connection id on that interface.

Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: Greg Kroah-Hartman <greg@kroah.com>