x86: Don't build call64 and setjmp on 64-bit

These are currently not supported. Calling 64-bit code from 64-bit U-Boot is
much simpler, so this code is not needed. setjmp() is not yet implemented for
64-bit.

Signed-off-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>
diff --git a/arch/x86/lib/bootm.c b/arch/x86/lib/bootm.c
index e5e63f6..3c3d9e1 100644
--- a/arch/x86/lib/bootm.c
+++ b/arch/x86/lib/bootm.c
@@ -155,7 +155,14 @@
 			puts("Cannot boot 64-bit kernel on 32-bit machine\n");
 			return -EFAULT;
 		}
+		/* At present 64-bit U-Boot does not support booting a
+		 * kernel.
+		 * TODO(sjg@chromium.org): Support booting both 32-bit and
+		 * 64-bit kernels from 64-bit U-Boot.
+		 */
+#if !CONFIG_IS_ENABLED(X86_64)
 		return cpu_jump_to_64bit(setup_base, load_address);
+#endif
 	} else {
 		/*
 		* Set %ebx, %ebp, and %edi to 0, %esi to point to the