[63/77] Simplifications after type switch

[63/77] Simplifications after type switch

This patch makes a few simplifications after the previous
mechanical machine_mode->scalar_int_mode change.

2017-08-30  Richard Sandiford  <richard.sandiford@linaro.org>
	    Alan Hayward  <alan.hayward@arm.com>
	    David Sherwood  <david.sherwood@arm.com>

gcc/
	* expmed.c (extract_high_half): Use scalar_int_mode and remove
	assertion.
	(expmed_mult_highpart_optab): Likewise.
	(expmed_mult_highpart): Likewise.

Co-Authored-By: Alan Hayward <alan.hayward@arm.com>
Co-Authored-By: David Sherwood <david.sherwood@arm.com>
From-SVN: r251514