mx6: Distinguish mx6dual from mx6quad

Currently when we boot a mx6dual U-boot reports that it is a mx6quad.

Report it as MX6D instead:

CPU:   Freescale i.MX6D rev1.2 at 792 MHz

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
Acked-by: Stefano babic <sbabic@denx.de>
Acked-by: Otavio Salvador <otavio@ossystems.com.br>
diff --git a/arch/arm/include/asm/arch-imx/cpu.h b/arch/arm/include/asm/arch-imx/cpu.h
index 8c725e2..a35940e 100644
--- a/arch/arm/include/asm/arch-imx/cpu.h
+++ b/arch/arm/include/asm/arch-imx/cpu.h
@@ -10,3 +10,4 @@
 #define MXC_CPU_MX6DL		0x61
 #define MXC_CPU_MX6SOLO		0x62
 #define MXC_CPU_MX6Q		0x63
+#define MXC_CPU_MX6D		0x64