Support Intel iGPU frequency configuration

[flexagoon]

TLP has the following options:

INTEL_GPU_MIN_FREQ_ON_AC=0
INTEL_GPU_MIN_FREQ_ON_BAT=0
INTEL_GPU_MAX_FREQ_ON_AC=0
INTEL_GPU_MAX_FREQ_ON_BAT=0
INTEL_GPU_BOOST_FREQ_ON_AC=0
INTEL_GPU_BOOST_FREQ_ON_BAT=0

Set the min/max/turbo frequency for the Intel GPU. Possible values depend on your hardware. See the output of tlp-stat -g for available frequencies.

It doesn't seem like it's possible to configure this with Tuned currently. Would be great to have support for this.