imx/mx3: rename files defining a machine to mach-$mach.c

While at it remove some superfluous parenthesis.

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>
Cc: Sascha Hauer <kernel@pengutronix.de>
Cc: Russell King <linux@arm.linux.org.uk>
Cc: Daniel Mack <daniel@caiaq.de>
Cc: Fabio Estevam <fabio.estevam@freescale.com>
Cc: Valentin Longchamp <valentin.longchamp@epfl.ch>