[OpenMP][NVPTX] Fixed a compilation error in deviceRTLs caused by unsupported feature in release verion of LLVM

`ptx71` is not supported in release version of LLVM yet. As a result,
the support of CUDA 11.2 and CUDA 11.1 caused a compilation error as mentioned
in D97004. Since the support in D97004 is just a WA for releease, and we'll not
use it in the near future, using `ptx70` for CUDA 11 is feasible.

Reviewed By: jdoerfert

Differential Revision: https://reviews.llvm.org/D97195

(cherry picked from commit f6c2984)

Author: shiltian

openmp/libomptarget/deviceRTLs/nvptx/CMakeLists.txt

@@ -153,7 +153,7 @@ add_custom_target(omptarget-nvptx-bc)
 # This map is from clang/lib/Driver/ToolChains/Cuda.cpp.
 # The last element is the default case.
 set(cuda_version_list 112 111 110 102 101 100 92 91 90 80)
-set(ptx_feature_list 71 71 70 65 64 63 61 61 60 42)
+set(ptx_feature_list 70 70 70 65 64 63 61 61 60 42)
 # The following two lines of ugly code is not needed when the minimal CMake
 # version requirement is 3.17+.
 list(LENGTH cuda_version_list num_version_supported)