ARM: mx31pdk: Fix build by passing IMX_HAVE_PLATFORM_MXC_MMC

mx31pdk target fails to build:

  CC      init/version.o
  LD      init/built-in.o
  LD      .tmp_vmlinux1
arch/arm/mach-imx/built-in.o: In function `mx31_3ds_init':
mach-mx31_3ds.c:(.init.text+0x548): undefined reference to `imx_add_mxc_mmc'
mach-mx31_3ds.c:(.init.text+0x69c): undefined reference to `imx31_mxc_mmc_data'
make: *** [.tmp_vmlinux1] Error

Fix this by passsing IMX_HAVE_PLATFORM_MXC_MMC option.
Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>

arch/arm/mach-imx/Kconfig

@@ -449,6 +449,7 @@ config MACH_MX31_3DS
 	select IMX_HAVE_PLATFORM_IMX_UART
 	select IMX_HAVE_PLATFORM_IPU_CORE
 	select IMX_HAVE_PLATFORM_MXC_EHCI
+	select IMX_HAVE_PLATFORM_MXC_MMC
 	select IMX_HAVE_PLATFORM_MXC_NAND
 	select IMX_HAVE_PLATFORM_SPI_IMX
 	select MXC_ULPI if USB_ULPI