ximgproc: FBSFilter fails with eps over

[tomoaki0705]

System information (version)

• OpenCV => recent 3.4 ( cabad90 ) + contrib ( f9c8cb8 )
• Operating System / Platform => Ubuntu 18.04 (Aarch64) Jetson Nano
• Compiler => GCC 7.5.0

Detailed description

Test FastBilateralSolverTest.ReferenceAccuracy fails but hard to judge with human eys

$ ./opencv_test_ximgproc --gtest_filter=FastBilateralSolverTest.ReferenceAccuracy
  :
[----------] 1 test from FastBilateralSolverTest
[ RUN      ] FastBilateralSolverTest.ReferenceAccuracy
#iterations:     25
estimated error: 0.00147801
#iterations:     25
estimated error: 0.000920876
#iterations:     25
estimated error: 0.0010467
/opencv_contrib/modules/ximgproc/test/test_fbs_filter.cpp:107: Failure
Expected: (cvtest::norm(res, ref, NORM_INF)) <= (1), actual: 41 vs 1
[  FAILED  ] FastBilateralSolverTest.ReferenceAccuracy (242 ms)
[----------] 1 test from FastBilateralSolverTest
  :
[  FAILED  ] 1 test, listed below:
[  FAILED  ] FastBilateralSolverTest.ReferenceAccuracy

• result image
  
• reference (from opencv_extra)
  
• diff of above 2 files
  

The test code is expecting bit-exact, but on platforms other than x86_64, I think bit-exact doesn't happen.
Loosening threshold is not really realistic, since diff 41 is bit too large (but this rarely happens)

I added a new comparison method in ts module, and modified to use that test when NOT on x86_64

I'll send a PR later

Steps to reproduce

Issue submission checklist

• I report the issue, it's not a question
• I checked the problem with documentation, FAQ, open issues,
  answers.opencv.org, Stack Overflow, etc and have not found solution
• I updated to latest OpenCV version and the issue is still there
• There is reproducer code and related data files: videos, images, onnx, etc