EINJ, Documentation: Update EINJ kernel doc

Update EINJ kernel document to include how to inject CXL protocol error
types, build the kernel to include CXL error types, and give an example
injection.

Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
Signed-off-by: Ben Cheatham <Benjamin.Cheatham@amd.com>
Link: https://lore.kernel.org/r/20240311142508.31717-5-Benjamin.Cheatham@amd.com


Signed-off-by: Dan Williams <dan.j.williams@intel.com>