ARM: imx6: fix SMP compilation again

My earlier patch 1fc593f ("ARM: imx: build i.MX6 functions
only when needed") fixed a problem with building an i.MX5 kernel,
but now the problem has returned for the case where we allow
ARMv6K SMP builds in multiplatform. With CONFIG_CPU_V7 disabled,
but i.MX3 and SMP enabled, we get this build error:

arch/arm/mach-imx/built-in.o: In function `v7_secondary_startup':
:(.text+0x5124): undefined reference to `v7_invalidate_l1'

This puts the code inside of an "ifdef CONFIG_SOC_IMX6" to hopefully
do the right thing in all configurations.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Shawn Guo <shawn.guo@freescale.com>

arch/arm/mach-imx/Makefile

@@ -93,9 +93,11 @@ obj-$(CONFIG_HAVE_IMX_ANATOP) += anatop.o
 obj-$(CONFIG_HAVE_IMX_GPC) += gpc.o
 obj-$(CONFIG_HAVE_IMX_MMDC) += mmdc.o
 obj-$(CONFIG_HAVE_IMX_SRC) += src.o
+ifdef CONFIG_SOC_IMX6
 AFLAGS_headsmp.o :=-Wa,-march=armv7-a
 obj-$(CONFIG_SMP) += headsmp.o platsmp.o
 obj-$(CONFIG_HOTPLUG_CPU) += hotplug.o
+endif
 obj-$(CONFIG_SOC_IMX6Q) += clk-imx6q.o mach-imx6q.o
 obj-$(CONFIG_SOC_IMX6SL) += clk-imx6sl.o mach-imx6sl.o
 obj-$(CONFIG_SOC_IMX6SX) += clk-imx6sx.o mach-imx6sx.o