[og7] Adjust k80 resources

[Cesar Philippidis]

I've pushed this patch to openacc-gcc-7-branch to teach the libgomp
nvptx plugin how to cope with the hardware resources on K80 boards. K80
boards have two physical GPUs on a single board. Consequently, the CUDA
driver reports that 2x the amount of registers and shared memory are
available on those GPUs. But that's not true if only a single GPU is
being utilized. Consequently, this prevented the runtime from informing
the user that that K80 does not have sufficient hardware resources to
execute certain offloaded kernels.

Unfortunately, I don't have a test case which reproduce this failure,
but it does show up in various OpenACC tests such as cloverleaf. I'll
try to create a reduced test case that uses a lot of hardware registers
later.

Cesar
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