Function dt_cg_field_get

* If the result of a "." or "->" operation is a bit-field, we use this routine * to generate an epilogue to the load instruction that extracts the value. In * the diagrams below the "ld??" is the load instruction that is generated to * load the containing word that is generating prior to calling this function. * * Epilogue for unsigned fields: Epilogue for signed fields: * * ldu? [r1], r1