ACPI: Enable C3 even when PM2_control is zero

On systems that do not have pm2_control_block, we cannot really use
ARB_DISABLE before C3. We used to disable C3 totally on such systems.

To be compatible with Windows, we need to enable C3 on such systems now.
We just skip ARB_DISABLE step before entering the C3-state and assume
hardware is handling things correctly. Also, ACPI spec is not clear
about pm2_control is _needed_ for C3 or not.

We have atleast one system that need this to enable C3.

Signed-off-by: Venkatesh Pallipadi <venkatesh.pallipadi@intel.com>
Signed-off-by: Len Brown <len.brown@intel.com>