Initial SST SimEng integration.

[rahahahat]

This PR implements the SST wrapper needed for successful integration with SST. It also adds support for conditional compilation through CMake and a custom testing framework used for testing the integration. Documentation for running and building SimEng with the SST integration enabled is temporarily available here. It will be added to the source at a later stage.

The custom SST testing framework exposes two main testing macros (TEST_GROUP and TEST_CASE) along with multiple evaluation macros. The framework runs sst with a config file specified by the TEST_GROUP and captures the stdout of the child process, injecting it to individual test cases and allowing the user to define multiple checks on that captured output through the use of evaluation macros. The testing framework also exposes a parser, which parses the output of the sst simulation and turns the output into structs, which can then be used by the tests. Currently, there are two formats:

[SimEng:SSTDebug] MemRead-read-<type=request|response>-<request ID>-cycle-<cycle count>-data-<value>.

The entire output is parsed into:

struct ParsedMemRead {
  uint64_t reqId_;
  uint64_t startCycle_;
  uint64_t endCycle_;
  uint64_t data_;
  uint64_t numReqs_;
};

[SimEng::SSTDebug] OutputLine-<text>. 

This format is parsed, and <text> is extracted by the parser.

The testing framework adds 2 new compile definitions to the initial CMake configuration command:

• -DSIMENG_ENABLE_SST_TESTS: This definition enables SST Tests only if -DSIMENG_ENABLE_TESTS is defined.
• -DSST_TESTS_MODEL_CONFIG_PATH: This definition is optional; using this compile definition, the user can specify a SimEng model config. However, if not provided. All tests will, by default, use a64fx-sst.yaml model configuration.

There are 2 sst configuration files added in the testing framework: fastL1ForBinaries.py and fastL1withParams_config.py.
Arguments can be passed to these sst configuration files via test cases using a key value format, i.e. key=value.
Currently, 6 argument types can be passed by test cases and are replaced in the configuration files, ultimately to be passed to SimEngCoreWrapper:

• execBin : This is the path to an executable executed by SSTSimEng. Example: execBin=/ab/cd/exec.
• args: These are all the args passed to the executable. Example: args=10 20 50.
• withSrc: This signals if the test will pass a string of instructions to be assembled by LLVM. Example: withSrc=<True|False>.
• source: This contains all instructions to be assembled by LLVM. Example: source=mov x1, #0.
• heap: This contains comma-separated values, which will be used to initialise the heap. Example: heap=10,20,30.
• clw: This contains the cache line width in bytes: Example: clw=64.

[dANW34V3R]

General structure is still looking good. A short PR description needed, you could use the one from #250.

Main points are; the need for the binaries and the need for all of the conditional compilation. I have left comments for both of these.

[dANW34V3R]

Nice work. Removal of most of the ifdefs makes the code much more readable

[jj16791]

Looks good to me