treewide: simplify the active-low line property

treewide: simplify the active-low line property

Unlike line direction - where input and output modes are equal, no signal
inversion (active-high) is the natural state of the line while active-low
is less likely. Let's drop the ACTIVE_STATE enum treewide and provide a
boolean property for lines - is_active_low() - to reflect that fact. This
function returning false means the line is "active-high".

Signed-off-by: Bartosz Golaszewski <bgolaszewski@baylibre.com>