mx6qsabre_common: Let mmc partition be board specific

commit 49ea0ff5 (49ea0ff5) introduced CONFIG_SYS_MMC_ENV_PART into mx6qsabresd.h
to store the mmc partition, but in order for it to have effect we should place
it into 'mmcpart' variable.

Also add CONFIG_SYS_MMC_ENV_PART into mx6qsabreauto.h.

Signed-off-by: Fabio Estevam <fabio.estevam@freescale.com>
diff --git a/include/configs/mx6qsabre_common.h b/include/configs/mx6qsabre_common.h
index cda4512..d76357c 100644
--- a/include/configs/mx6qsabre_common.h
+++ b/include/configs/mx6qsabre_common.h
@@ -91,7 +91,7 @@
 	"fdt_high=0xffffffff\0"	  \
 	"initrd_high=0xffffffff\0" \
 	"mmcdev=" __stringify(CONFIG_SYS_MMC_ENV_DEV) "\0" \
-	"mmcpart=1\0" \
+	"mmcpart=" __stringify(CONFIG_SYS_MMC_ENV_PART) "\0" \
 	"mmcroot=" CONFIG_MMCROOT " rootwait rw\0" \
 	"mmcargs=setenv bootargs console=${console},${baudrate} " \
 		"root=${mmcroot}\0" \