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/chromebook_link.h b/include/configs/chromebook_link.h
index 5265787..f2d798a 100644
--- a/include/configs/chromebook_link.h
+++ b/include/configs/chromebook_link.h
@@ -16,4 +16,7 @@
 #include <configs/x86-common.h>
 #include <configs/x86-chromebook.h>
 
+#define CONFIG_ENV_SECT_SIZE		0x1000
+#define CONFIG_ENV_OFFSET		0x003f8000
+
 #endif	/* __CONFIG_H */