xtensa: clean up exception handler prototypes

Exception handlers are currently passed as void pointers because they
may have one or two parameters. Only two handlers uses the second
parameter and it is available in the struct pt_regs anyway. Make all
handlers have only one parameter, introduce xtensa_exception_handler
type for handlers and use it in trap_set_handler.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>

xtensa: move S32C1I self-test to a separate file

The test is not called from any of the setup functions, so there's no
reason keeping it in the setup.c. Move it to s32c1i_selftest.c and drop
related #include directives.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>