x86: make LOAD_FROM_32_BIT visible for platforms

This option is useful not only for development, but for the platforms
where U-Boot is run from custom ROM bootloader. For example, Intel
Edison is that board.

Make this option visible that platforms can select it if needed.
Signed-off-by: NAndy Shevchenko <andriy.shevchenko@linux.intel.com>
Reviewed-by: NBin Meng <bmeng.cn@gmail.com>

arch/x86/Kconfig

@@ -195,6 +195,14 @@ config SYS_X86_START16
 	depends on X86_RESET_VECTOR
 	default 0xfffff800
 
+config X86_LOAD_FROM_32_BIT
+	bool "Boot from a 32-bit program"
+	help
+	  Define this to boot U-Boot from a 32-bit program which sets
+	  the GDT differently. This can be used to boot directly from
+	  any stage of coreboot, for example, bypassing the normal
+	  payload-loading feature.
+
 config BOARD_ROMSIZE_KB_512
 	bool
 config BOARD_ROMSIZE_KB_1024

arch/x86/cpu/start.S

@@ -18,14 +18,6 @@
 #include <generated/generic-asm-offsets.h>
 #include <generated/asm-offsets.h>
 
-/*
- * Define this to boot U-Boot from a 32-bit program which sets the GDT
- * differently. This can be used to boot directly from any stage of coreboot,
- * for example, bypassing the normal payload-loading feature.
- * This is only useful for development.
- */
-#undef LOAD_FROM_32_BIT
-
 .section .text
 .code32
 .globl _start
@@ -76,7 +68,7 @@ _start:
 	/* Save table pointer */
 	movl	%ecx, %esi
 
-#ifdef LOAD_FROM_32_BIT
+#ifdef CONFIG_X86_LOAD_FROM_32_BIT
 	lgdt	gdt_ptr2
 #endif
 
@@ -233,7 +225,7 @@ multiboot_header:
 	/* entry addr */
 	.long	CONFIG_SYS_TEXT_BASE
 
-#ifdef LOAD_FROM_32_BIT
+#ifdef CONFIG_X86_LOAD_FROM_32_BIT
 	/*
 	 * The following Global Descriptor Table is just enough to get us into
 	 * 'Flat Protected Mode' - It will be discarded as soon as the final