Correct/Simplify ignore wide residue message handling

Correct/Simplify ignore wide residue message handling

aic79xx.c:
	In ahd_handle_ign_wide_residue():
	o Use SCB_XFERLEN_ODD SCB field to determine transfer
	  "oddness" rather than the DATA_COUNT_ODD logic.
	  SCB_XFERLEN_ODD is toggled on every ignore wide
	  residue message so that multiple ignore wide residue
	  messages for the same transaction are properly supported.
	o If the sg list has been exausted, the sequencer
	  doesn't bother to update the residual data count
	  since it is known to be zero.  Perform the zeroing
	  manually before calculating the remaining data count.
	o Use multibyte in/out macros instead of shifting/masking
	  by hand.

aic79xx_inline.h:
	In ahd_setup_scb_common(), setup the SCB_XFERLEN_ODD field.

aic79xx.reg:
	Use the SCB_TASK_ATTRIBUTE field as a bit field in the
	non-packetized case.  We currently only define one bit,
	SCB_XFERLEN_ODD.

	Remove the ODD_SEG bit field that was used to carry the odd
	transfer length information through the SG cache.  This
	is obviated by SCB_XFERLEN_ODD field.

	Remove the DATA_COUNT_ODD scratch ram byte that was used
	dynamicaly compute data transfer oddness.  This is obviated
	by SCB_XFERLEN_ODD field.

aic79xx.seq:
	Remove all updates to the DATA_COUNT_ODD scratch ram field.
	Remove all uses of ODD_SEG.  These two save quite a few
	sequencer instructions.

	Use SCB_XFERLEN_ODD to validate the end of transfer
	ignore wide residue message case.