fix: gpio_input_get() fails to compile in Arduino-ESP32 parallel mode; replace with REG_READ(GPIO_IN_REG)

[skele6011]

Problem

In Arduino-ESP32 environments, gpio_input_get() used in readByte()
fails to compile when using 8-bit parallel mode (TFT_PARALLEL_8_BIT).
This is due to the Arduino-ESP32 core not cleanly exposing every IDF
function. This means gpio_input_get() is not properly resolved in the Arduino
build chain, causing a compile error.

Fix

Replace all three calls to gpio_input_get() with REG_READ(GPIO_IN_REG),
which reads the GPIO input register directly at the hardware level with
no dependency on the IDF abstraction layer.

The logic is identical, three reads to allow for bus access time — only
the mechanism changes.

Environment Tested

• ESP32-D (DevKit)
• Arduino-ESP32 core
• Arduino IDE
• 8-bit parallel display (ILI9486, 3.5" TFT)

Notes

The library does not compile at all without this fix in the above environment. REG_READ(GPIO_IN_REG) is the correct low-level equivalent and works reliably.
This fixes issues like the ones here