[SPIR-V] support externally initialized non-floating-point column-major matrices

[farzonl]

The following code is supported when targeting DirectX but is gated by an error when targeting spirv
https://hlsl.godbolt.org/z/zr9P6GKhx

struct A {
  RWStructuredBuffer<int3x2> Buf;
};

A a1;
A a2;

[numthreads(1,1,1)]
void main() {
  int3x2 m = a1.Buf[0];
  a2.Buf[0] = m * 2;
}

DirectXShaderCompiler/tools/clang/test/CodeGenSPIRV/vk.layout.non-fp-matrix.array.struct.error.hlsl

Line 37 in b87d15d

// CHECK: :11:21: error: externally initialized non-floating-point column-major matrices not supported yet

DirectXShaderCompiler/tools/clang/test/CodeGenSPIRV/vk.layout.non-fp-matrix.error.hlsl

Line 19 in b87d15d

// CHECK: :6:5: error: externally initialized non-floating-point column-major matrices not supported yet

For now marking these as not supported for the offload test suite when targeting spirv.