selftests/ftrace: Update synthetic event syntax errors

Some of the synthetic event errors and positions have changed in the
code - update those and add several more tests.

Also add a runtime check to ensure that the kernel supports dynamic
strings in synthetic events, which these tests require.

Fixes: 81ff92a93d95 (selftests/ftrace: Add test case for synthetic
event syntax errors)

Reported-by: Masami Hiramatsu <mhiramat@kernel.org>
Signed-off-by: Tom Zanussi <zanussi@kernel.org>