ACPI: DPTF: Fix reading of attributes

The current assumption that methods to read PCH FIVR attributes will
return integer, is not correct. There is no good way to return integer
as negative numbers are also valid.

These read methods return a package of integers. The first integer returns
status, which is 0 on success and any other value for failure. When the
returned status is zero, then the second integer returns the actual value.

This change fixes this issue by replacing acpi_evaluate_integer() with
acpi_evaluate_object() and use acpi_extract_package() to extract results.

Fixes: 2ce6324e ("ACPI: DPTF: Add PCH FIVR participant driver")
Signed-off-by: Srinivas Pandruvada <srinivas.pandruvada@linux.intel.com>
Cc: 5.10+ <stable@vger.kernel.org> # 5.10+
Signed-off-by: Rafael J. Wysocki <rafael.j.wysocki@intel.com>