x86: qemu: Add missing DECLARE_GLOBAL_DATA_PTR in e820.c

DECLARE_GLOBAL_DATA_PTR is missing which causes 64-bit build error.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

arch/x86/cpu/qemu/e820.c

@@ -7,6 +7,8 @@
 #include <common.h>
 #include <asm/e820.h>
 
+DECLARE_GLOBAL_DATA_PTR;
+
 unsigned install_e820_map(unsigned max_entries, struct e820entry *entries)
 {
 	entries[0].addr = 0;