Add support for hammerhead magnetic lid sensor

Re-use existing N770 sliding cover functionality to handle also
magnetic lid sensor available in hammerhead.

When the lid is closed: ui is locked, display blanked and further
display state changes are denied (even power key will not turn on
the display).

When the lid is opened: display is unblanked and normal display
state changes are allowed again.

[mce] Add support for hammerhead magnetic lid sensor. Fixes JB#21639
Remove unused code

Were accidentally left in after battery device detection changes.
Merge pull request #200 from spiiroin/hammerhead_lid_cover_sensor

Add support for hammerhead magnetic lid sensor