eeepc-laptop: support for super hybrid engine (SHE)

The older eeepc-acpi driver allowed to control the SHE performance
preset through a ACPI function for just this purpose. SHE underclocks
and undervolts the FSB and undervolts the CPU (at preset 2,
"powersave"), or slightly overclocks the CPU (at preset 0,
"performance"). Preset 1 is the default setting with default clocks and
voltage.

The new eeepc-laptop driver doesn't support it anymore.
The attached patch adds support for it to eeepc-laptop. It's very
straight-forward and almost trivial.

Signed-off-by: Grigori Goronzy <greg@chown.ath.cx>
Signed-off-by: Corentin Chary <corentincj@iksaif.net>
Signed-off-by: Len Brown <len.brown@intel.com>