arm: mach-k3: am6_init: Use CONFIG_TI_I2C_BOARD_DETECT

We only want to call do_board_detect() if CONFIG_TI_I2C_BOARD_DETECT
is set. Same as done for am64.

This makes it possible to add a custom am65 based board design to
U-Boot that does not use this board detection mechanism.

Signed-off-by: Christian Gmeiner <christian.gmeiner@gmail.com>