[amdgcn] Scale number of threads/workers with VGPR usage

[amdgcn] Scale number of threads/workers with VGPR usage

2020-01-31  Kwok Cheung Yeung  <kcy@codesourcery.com>

	gcc/
	* config/gcn/mkoffload.c (process_asm): Add sgpr_count and vgpr_count
	to definition of hsa_kernel_description.  Parse assembly to find SGPR
	and VGPR count of kernel and store in hsa_kernel_description.

	libgomp/
	* plugin/plugin-gcn.c (struct hsa_kernel_description): Add sgpr_count
	and vgpr_count fields.
	(struct kernel_info): Add a field for a hsa_kernel_description.
	(run_kernel): Reduce the number of threads/workers if the requested
	number would require too many VGPRs.
	(init_basic_kernel_info): Initialize description field with
	the hsa_kernel_description entry for the kernel.