openacc: Fix mkoffload SGPR/VGPR count parsing for HSACO v3

openacc: Fix mkoffload SGPR/VGPR count parsing for HSACO v3

If an offload kernel uses a large number of VGPRs, AMD GCN hardware may
need to limit the number of threads/workers launched for that kernel.
The number of SGPRs/VGPRs in use is detected by mkoffload and recorded in
the processed output.  The patterns emitted detailing SGPR/VGPR occupancy
changed between HSACO v2 and v3 though, so this patch updates parsing
to account for that.

2020-09-08  Julian Brown  <julian@codesourcery.com>

gcc/
	* config/gcn/mkoffload.c (process_asm): Initialise regcount.  Update
	scanning for SGPR/VGPR usage for HSACO v3.