efi_loader: Increase number of configuration tables to 16

At present the number of configuration tables is set to 2. By
looking at which tables the Linux EFI stub or iPXE can process,
it looks 16 is a reasonable number.
Signed-off-by: NBin Meng <bmeng.cn@gmail.com>
Reviewed-by: NHeinrich Schuchardt <xypron.glpk@gmx.de>

lib/efi_loader/efi_boottime.c

@@ -43,7 +43,7 @@ static bool efi_is_direct_boot = true;
  * In most cases we want to pass an FDT to the payload, so reserve one slot of
  * config table space for it. The pointer gets populated by do_bootefi_exec().
  */
-static struct efi_configuration_table __efi_runtime_data efi_conf_table[2];
+static struct efi_configuration_table __efi_runtime_data efi_conf_table[16];
 
 #ifdef CONFIG_ARM
 /*