Add access to init functions from TFT.cpp

[ghost]

My TFT display has its Red and Blue channels inverted.

There are several mentions of this issue online, specially on Adafruit related repos, and none offers a straight solution other than digging through their libraries and changing hard coded definitions.

This proposed change overloads the TFT.begin() method to access the different initialization functions found in Adafruit_ST7735.cpp.

To change from RGB to BGR:

TFT.begin(INITR_BLACKTAB);

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