arm: mx23: recognise stmp378x as mx23

Adding the machine_is_* line was forgotten when converting mach-stmp378x to
mach-mxs.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Signed-off-by: Shawn Guo <shawn.guo@linaro.org>
Cc: stable@kernel.org
1 file changed