Atari SIO communication is broken starting with esp32_platform_version 6.11.0

[pdaehne]

With this commit, someone from Espressif removed the default pull-up resistor on serial rx lines. This went into esp32_platform_version 6.11.0 and breaks the Atari SIO communication, because the SIO signal goes through U4 on the Fujinet hardware, a 74LS07 with open-collector output which is floating now. I was able to fix that problem by putting a "gpio_pullup_en((gpio_num_t)rx);" call after the "uart_set_pin" call in "fnUART.cpp". Unfortunately, I do not have much insight into the Fujinet firmware and cannot create a proper pull request.