ar71xx: rbspi: fix RB wAP AC gpio conflict and LED

ar71xx: rbspi: fix RB wAP AC gpio conflict and LED

e15c63a37574bd15ce3a6636c2f04741ab76f7b9 introduced code that was trying
to register GPIO 1 as both an LED and a button. The OEM source makes it
clear that LED1 is not wired to the SoC GPIOs. GPIO 1 is the reset button.

Furthermore the (green) power led default state should also be defined,
(matching OEM source), and it should be used by diag.sh since it's
currently the only software-controllable LED.

This patch fixes these issues and renames the corresponding #defines for
clarity

Signed-off-by: Thibaut VARÈNE <hacks@slashdirt.org>
(cherry picked from commit e99f760235bb45716018faab52d31ce8165f49a0)