[nvptx] Add missing t-omp-device isas

[nvptx] Add missing t-omp-device isas

In t-omp-device we list isas that can be used in omp declare variant like so:
...
  #pragma omp declare variant (f30) match (device={isa("sm_30")})
...
and in nvptx_omp_device_kind_arch_isa we handle them.

Update both to reflect the current list of isas.

Tested on x86_64-linux with nvptx accelerator.

gcc/ChangeLog:

2022-02-23  Tom de Vries  <tdevries@suse.de>

	* config/nvptx/nvptx.cc (nvptx_omp_device_kind_arch_isa): Handle
	sm_70, sm_75 and sm_80.
	* config/nvptx/t-omp-device: Add sm_53, sm_70, sm_75 and sm_80.

Co-Authored-By: Tobias Burnus <tobias@codesourcery.com>