efi: stub: Pass EFI system table address to U-Boot payload

This updates the EFI stub codes to pass UEFI BIOS's system table
address to U-Boot payload so that U-Boot can utilize it.

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/lib/efi/efi_stub.c b/lib/efi/efi_stub.c
index 1b495ec..12e3d63 100644
--- a/lib/efi/efi_stub.c
+++ b/lib/efi/efi_stub.c
@@ -277,6 +277,7 @@
 	struct efi_entry_memmap map;
 	struct efi_gop *gop;
 	struct efi_entry_gopmode mode;
+	struct efi_entry_systable table;
 	efi_guid_t efi_gop_guid = EFI_GOP_GUID;
 	efi_uintn_t key, desc_size, size;
 	efi_status_t ret;
@@ -335,6 +336,9 @@
 		return ret;
 	}
 
+	table.sys_table = (ulong)sys_table;
+	add_entry_addr(priv, EFIET_SYS_TABLE, &table, sizeof(table), NULL, 0);
+
 	ret = boot->exit_boot_services(image, key);
 	if (ret) {
 		/*