Unify device selection code.

[CAHEK7]

Currently some of the tests are using direct string comparison to check if the tests are available for the particular device, but that is error prone and does not match to the previous CTest device selection algorithm. (unfortunately we have to keep backward compatibility for Ctest-Gtest transition period, later it has to be refactored as well)

For example

MIOpen/test/gtest/layernorm.cpp

Line 54 in 3183bb2

if((miopen::StartsWith(handle.GetDeviceName(), "gfx908") ||

has that sort of check.

In order to improve tests quality we have to switch to the mechanism introduced in #2605 for all the google tests.

All the tests should have an IsTestSupportedForDevice function and use functions and enums to select proper devices.