gpio: of: Reflect decoupling of open collector and active low/high

Commit 4c0facddb7d8 ("gpio: core: Decouple open drain/source flag with
active low/high") decoupled the open collector outputs from active
low/high but did not update the documentation.

Update the device tree documentation to correctly reflect this new
separation between the two concepts.

Signed-off-by: Charles Keepax <[e-mail]>
Acked-by: Laxman Dewangan <[e-mail]>
Signed-off-by: Linus Walleij <[e-mail]>

Documentation/devicetree/bindings/gpio/gpio.txt

···
 Optional standard bitfield specifiers for the last cell:
 
 - Bit 0: 0 means active high, 1 means active low
-- Bit 1: 1 means single-ended wiring, see:
+- Bit 1: 0 mean push-pull wiring, see:
+           https://en.wikipedia.org/wiki/Push-pull_output
+         1 means single-ended wiring, see:
            https://en.wikipedia.org/wiki/Single-ended_triode
-	   When used with active-low, this means open drain/collector, see:
+- Bit 2: 0 means open-source, 1 means open drain, see:
            https://en.wikipedia.org/wiki/Open_collector
-	   When used with active-high, this means open source/emitter
 
 1.1) GPIO specifier best practices
 ----------------------------------