sysc: avoid using orpsoc internal classes directly

The problem with using the internal classes directly is
that you have to use the internally generated name,
this in itself is perhaps not such a big issue, the issue
is that the internal name changes when the underlaying verilog
design changes.
This works around this by using the classes through the
top module, which is part of the external api.
scripts/gccregression: fix one-off in GCC_C_TESTS_START

Tests would be restarted at the next test after
GCC_C_TESTS_START instead of at GCC_C_TESTS_START.
Merge pull request #4 from skristiansson/for-julius

fixes related to running the cycle accurate simulator