x86: acpi: Align FACS table to a 64 byte boundary

Per ACPI spec, the FACS table address must be aligned to a 64 byte
boundary (Windows checks this, but Linux does not).

Signed-off-by: Bin Meng <bmeng.cn@gmail.com>
Reviewed-by: Stefan Roese <sr@denx.de>
Tested-by: Stefan Roese <sr@denx.de>
Reviewed-by: Simon Glass <sjg@chromium.org>