sandbox: building fails with GENERATE_ACPI_TABLE=y, ACPIGEN=n

[Heinrich Schuchardt]

Hello Simon,

sandbox_defconfig with ACPIGEN=n fails to build.

We should not have two customizable symbols if the one cannot be set to
no without the other.

* GENERATE_ACPI_TABLE
* ACPIGEN

It should be possible to build the sandbox without ACPI tables to test
UEFI binaries using device-trees. This requires to get test/dm/Makefile
right.

Best regards

Heinrich