x86: edison: Enable SD slot

Enable SD slot on Intel Edison platform.

By default firmware doesn't put device on active state. Thus,
we have to do this explicitly.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/configs/edison_defconfig b/configs/edison_defconfig
index 4687544..cac6e42 100644
--- a/configs/edison_defconfig
+++ b/configs/edison_defconfig
@@ -4,6 +4,7 @@
 CONFIG_VENDOR_INTEL=y
 CONFIG_TARGET_EDISON=y
 CONFIG_SMP=y
+CONFIG_BOARD_EARLY_INIT_R=y
 CONFIG_LAST_STAGE_INIT=y
 CONFIG_HUSH_PARSER=y
 # CONFIG_CMDLINE_EDITING is not set