mx7: Do not call lcdif_power_down() in the SPL case

Like it was done on imx6 in commit 9236269d ("imx: mx6: Fix
implementantion reset_misc")

Do not call lcdif_power_down() in the SPL case to fix the following
build error:

  LD      spl/u-boot-spl
  MKIMAGE u-boot.img
arch/arm/mach-imx/built-in.o: In function `reset_misc':
/home/fabio/ossystems/u-boot/arch/arm/mach-imx/mx7/soc.c:372: undefined reference to `lcdif_power_down'
scripts/Makefile.spl:375: recipe for target 'spl/u-boot-spl' failed

Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Signed-off-by: Fabio Estevam <festevam@gmail.com>
Signed-off-by: Otavio Salvador <otavio@ossystems.com.br>
Reviewed-by: Peng Fan <peng.fan@nxp.com>