drm/i915/hwmon: Enable PL1 limit when writing limit value to HW

Previous documentation suggested that the PL1 power limit is always enabled
in HW. However we now find this not to be the case on some platforms (such
as ATSM). Therefore enable the PL1 power limit (by setting the enable bit)
when writing the PL1 limit value to HW.

Bspec: 51864

Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230216164944.2366150-3-ashutosh.dixit@intel.com