ARM: uniphier: default to environment in eMMC

Of the several boot devices supported, it looks like the eMMC is the
most commonly used.  Enable CONFIG_ENV_IS_IN_MMC by default.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/arch/arm/mach-uniphier/boot-mode/boot-mode.c b/arch/arm/mach-uniphier/boot-mode/boot-mode.c
index 0547762..cf39bf5 100644
--- a/arch/arm/mach-uniphier/boot-mode/boot-mode.c
+++ b/arch/arm/mach-uniphier/boot-mode/boot-mode.c
@@ -93,6 +93,11 @@
 	return -ENODEV;
 }
 
+int mmc_get_env_dev(void)
+{
+	return find_first_mmc_device();
+}
+
 static int do_mmcsetn(cmd_tbl_t *cmdtp, int flag, int argc, char * const argv[])
 {
 	int dev;