iwlwifi: don't export acpi functions unnecessarily

A couple of functions were exported from the acpi.c file
unnecessarily, since they are only used internally in that file.  Make
them static.

Signed-off-by: Luca Coelho <luciano.coelho@intel.com>
Link: https://lore.kernel.org/r/iwlwifi.20200926002540.6449efabcb8b.I030fa71253260f34b588951d78170551b633c046@changeid


Signed-off-by: Luca Coelho <luciano.coelho@intel.com>