[Arm] Cleanup IT attributes

[Arm] Cleanup IT attributes

A recent change to remove the movdi_vfp_cortexa8 meant that ldrd was used in
ITs block even when arm_restrict_it was enabled.  Rather than just fixing this
latent issue, change the default of predicable_short_it to "no" so that only
16-bit instructions need to be marked with it.  As a result there are far fewer
patterns that need the attribute, and omitting predicable_short_it is no longer
causing issues.

	* config/arm/arm.md (predicable_short_it): Change default to "no",
	improve documentation, remove uses that are identical to the default.
	(enabled_for_depr_it): Rename to enabled_for_short_it.
	* gcc/config/arm/arm-fixed.md (predicable_short_it): Remove default uses.
	* gcc/config/arm/ldmstm.md (predicable_short_it): Likewise.
	* gcc/config/arm/sync.md (predicable_short_it): Likewise.
	* gcc/config/arm/thumb2.md (predicable_short_it): Likewise.
	* gcc/config/arm/vfp.md (predicable_short_it): Likewise.

From-SVN: r254463