x86, setup: Fix typo "CONFIG_x86_64" in <asm/boot.h>

CONFIG_X86_64 was misspelled (wrong case), which caused the x86-64
kernel to advertise itself as more relocatable than it really is.
This could in theory cause boot failures once bootloaders start
support the new relocation fields.
Signed-off-by: NRobert P. J. Day <rpjday@crashcourse.ca>
Signed-off-by: NH. Peter Anvin <hpa@zytor.com>

arch/x86/include/asm/boot.h

@@ -16,7 +16,7 @@
 				& ~(CONFIG_PHYSICAL_ALIGN - 1))
 
 /* Minimum kernel alignment, as a power of two */
-#ifdef CONFIG_x86_64
+#ifdef CONFIG_X86_64
 #define MIN_KERNEL_ALIGN_LG2	PMD_SHIFT
 #else
 #define MIN_KERNEL_ALIGN_LG2	(PAGE_SHIFT+1)