* dcache: let ecc error and l2 corrupt raise load af

If CSR.smblockctl.cache_error_enable is disabled, ecc error and l2 corrupt
will not raise any exception.

* mem: enable cache error by default

* mem: support store ecc check, add ecc error csr

Support store / atom ecc check (early version)
Add ecc error csr to distingush ecc error and other access fault

Timing opt and unit tests to be added.