arm: Add support for VPR_REG in arm_class_likely_spilled_p

arm: Add support for VPR_REG in arm_class_likely_spilled_p

VPR_REG is the only register in its class, so it should be handled by
TARGET_CLASS_LIKELY_SPILLED_P, which is achieved by calling
default_class_likely_spilled_p.  No test fails without this patch, but
it seems it should be implemented.

Most of the work of this patch series was carried out while I was
working at STMicroelectronics as a Linaro assignee.

2022-02-22  Christophe Lyon  <christophe.lyon@arm.com>

	gcc/
	* config/arm/arm.cc (arm_class_likely_spilled_p): Handle VPR_REG.