Use textWrite's delay on smaller sizes with faster ARM processors

On Arduino Uno, this delay is only needed for text sizes 2 and 3.  Uno just isn't fast enough to send another SPI command before size 1 renders.

On Teensy 3.1 runs much faster, so this delay is needed to avoid garbled text.

Discussion and photos are here:

http://forum.pjrc.com/threads/24668-Teensy-3-*-Text-rendering-issue-with-RA8875-TFT-display