[arm][1/3] Rename mul64 attr to widen_mul64

[arm][1/3] Rename mul64 attr to widen_mul64

The mul64 attribute in types.md causes some confusion as it is used to represent
aarch32 instructions that do widening multiplication to generate 32->64 bit results.
But these types are shared with aarch64, which has native 64-bit multiplication operations.

Those are currently not properly represented, which I will fix in follow-up patches.
For now, this patch renames the mul64 attribute to widen_mul64 to more clearly communicate its meaning.

It mechanically updates all users of that name in config/arm/ (there are no users in config/aarch64).
There is thus no change in behaviour.

	* config/arm/types.md (mul64): Rename to...
	(widen_mul64): ... This.
	* config/arm/arm-generic.md: Rename mul64 to widen_mul64.
	* config/arm/cortex-a15.md: Likewise.
	* config/arm/cortex-a5.md: Likewise.
	* config/arm/cortex-a53.md: Likewise.
	* config/arm/cortex-a57.md: Likewise.
	* config/arm/cortex-a7.md: Likewise.
	* config/arm/cortex-m4.md: Likewise.
	* config/arm/exynos-m1.md: Likewise.
	* config/arm/marvell-pj4.md: Likewise.
	* config/arm/xgene1.md: Likewise.

From-SVN: r266471