Add fallback for ARM Windows fp16 detection.

[edgchen1]

Background: On a Windows ARM system, I observed that cpuinfo_has_arm_fp16_arith() started to return false after upgrading to a more recent cpuinfo version.

In #333, the initialization of cpuinfo_isa.fp16arith was updated to use IsProcessorFeaturePresent(PF_ARM_V82_FP16_INSTRUCTIONS_AVAILABLE). I suspect that this is not supported on older Windows versions.

This change adds a fallback path to set cpuinfo_isa.fp16arith the old way.

cpuinfo/src/arm/windows/init.c

Lines 205 to 208 in d3a86a8

	// Assume that Dot Product support implies FP16
	// arithmetics and RDM support. ARM manuals don't
	// guarantee that, but it holds in practice.
	cpuinfo_isa.fp16arith = dotprod;

[edgchen1]

Hi @tonybaloney, would you mind taking a look at this one?

[tonybaloney]

What chip is it?

[edgchen1]

What chip is it?

This was observed on an Azure Standard D16pds v5 machine with an Ampere Altra processor.