arch/intel64: prase multiboot2 header before revoking the lower memory

__revoke_low_memory() is called in intel64_lowsetup()

fixes b4b96a6 (PR apache#11758) in which the multiboot2 header was accessed
after revoking the low memory which caused page fault.

Signed-off-by: p-szafonimateusz <p-szafonimateusz@xiaomi.com>

arch/x86_64/src/intel64/intel64_start.c

@@ -125,16 +125,16 @@ void __nxstart(void)
       *dest++ = 0;
     }
 
-  /* Low-level, pre-OS initialization */
-
-  intel64_lowsetup();
-
 #ifdef CONFIG_ARCH_MULTIBOOT2
   /* Handle multiboot2 info */
 
   x86_64_mb2_config();
 #endif
 
+  /* Low-level, pre-OS initialization */
+
+  intel64_lowsetup();
+
   /* perform board-specific initializations */
 
   x86_64_boardinitialize();