staging/atomisp: add ACPI dependency

Without ACPI, some of the code fails to build:

media/atomisp/platform/intel-mid/atomisp_gmin_platform.c: In function 'atomisp_register_i2c_module':
media/atomisp/platform/intel-mid/atomisp_gmin_platform.c:174:7: error: dereferencing pointer to incomplete type 'struct acpi_device'

We could work around that in the code, but since we already have a hard
dependency on x86, adding the ACPI dependency seems to be the easiest
solution.

Fixes: a49d2536 ("staging/atomisp: Add support for the Intel IPU v2")
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Alan Cox <alan@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>