cmd: qfw: bring ACPI generation code into qfw core

Loading ACPI table from QEMU's fw_cfg interface is not x86 specific
(ARM64 may also make use of it). So move the code to common place.

Signed-off-by: Miao Yan <yanmiaobest@gmail.com>
Reviewed-by: Bin Meng <bmeng.cn@gmail.com>