tests/tcg/xtensa: allow testing big-endian cores

Don't disable all big-endian tests, instead check whether $(CORE) is
supported by the configured $(QEMU) and enable tests if it is.

Signed-off-by: Max Filippov <jcmvbkbc@gmail.com>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
3 files changed