acpi: enable writing ACPI tables on QEMU

Invoke write_acpi_tables() via EVT_LAST_STAGE_INIT on QEMU except on X86.
X86 calls write_acpi_tables() in write_tables().

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Simon Glass <sjg@chromium.org>

acpi: carve out qfw_acpi.c

Move the code related to copying tables from QEMU to a separate code
module.

Signed-off-by: Heinrich Schuchardt <heinrich.schuchardt@canonical.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
Reviewed-by: Ilias Apalodimas <ilias.apalodimas@linaro.org>