lookup is a bidirectional communication between the Xtensa and
the device implementing this interface. When the data method is
received by the device, the out_data pointer contains
out_width bits of data (from the Xtensa core) that the device
should read and take action upon.
As a response, the device should fill in in_width of bits in
the in_data buffer, providing the result of the lookup
back to the Xtensa instruction.