jaj: default I2C pins to output low

[dakejahl]

Summary

• Configure I2S connector GPIO pins (I2S0_SCLK, I2S0_DOUT, I2S0_DIN, I2S0_LRCLK, AUD_MCLK) to default output-low (0V) at boot via bootloader BCT
• Previously these pins were configured as high-impedance inputs, reverting to an undefined/high state when userspace GPIO control was released

Problem

When using I2S connector pins as GPIO via libgpio, pins revert to their bootloader default state on application exit or crash. A customer reported this caused unintended 3.3V on pins that need to be 0V by default.

Changes

Pinmux BCT (tegra234-mb1-bct-pinmux-p3767-dp-a03.dtsi):

• Set pull=NONE, tristate=DISABLE, enable-input=DISABLE on all 5 pins, configuring pads as actively driven outputs (matches existing gpio-output-low pin patterns like uart4_cts_ph6)

GPIO BCT (tegra234-mb1-bct-gpio-p3767-dp-a03.dtsi):

• Moved H,7 / I,0 / I,1 / I,2 / AC,6 from gpio-input to gpio-output-low

Test plan

• Re-flash board (BCT changes require full flash)
• Verify pins are output-low at boot before any app runs (gpioinfo / /sys/kernel/debug/gpio)
• Set pin high via GPIO app, kill app, confirm pin returns to 0V
• Confirm ark_i2s_gpio.dts overlay still works for normal GPIO usage