x86: Move CONFIG_ENV_IS_IN_SPI_FLASH to x86-common.h

Since all x86 boards use spi flash as its bootloader storage media,
it makes sense to make CONFIG_ENV_IS_IN_SPI_FLASH a common option.
So far only minnowmax board does not support it so undefine it in
its board configuration file.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Acked-by: Simon Glass <sjg@chromium.org>
diff --git a/include/configs/x86-common.h b/include/configs/x86-common.h
index 9571c65..07a5aca 100644
--- a/include/configs/x86-common.h
+++ b/include/configs/x86-common.h
@@ -207,7 +207,7 @@
 /*-----------------------------------------------------------------------
  * Environment configuration
  */
-#define CONFIG_ENV_IS_NOWHERE
+#define CONFIG_ENV_IS_IN_SPI_FLASH
 #define CONFIG_ENV_SIZE			0x01000
 
 /*-----------------------------------------------------------------------