imx/mx25: rename files defining a machine to mach-$mach.c

Signed-off-by: Uwe Kleine-König <u.kleine-koenig@pengutronix.de>

arch/arm/mach-mx25/Makefile

 obj-y				:= mm.o devices.o
 obj-$(CONFIG_ARCH_MX25)		+= clock.o
-obj-$(CONFIG_MACH_MX25_3DS)	+= mx25pdk.o
+obj-$(CONFIG_MACH_MX25_3DS)	+= mach-mx25pdk.o