efi_loader: 'EFI using ACPI tables at' should be debug message

The message "EFI using ACPI tables at %lx\n" is only of interest when
debugging. Make it a debug message.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>