Recent additions did not update these counts.

Seperated T3.5 from T3.6 as PWM and Analog counts are different

With the new beta boards, for those users who don't need an SDCard for
their project, it would be great to allow them to use the 6 IO pins
associated with the SDCARD for other purposes.  This would probably
require a cheap adapter, but these are nice signals to be able to be
used.  They include:

SPI1: SCK, MISO, MOSI, CS0-2
Serail2: TX/RX
Serial4: TX/RX
I2C1: SCL/SDA

This change adds support for GPIO, SPI, Serial2 and Serial4

https://forum.pjrc.com/threads/17469-millis%28%29-on-teensy-3?p=104924&viewfull=1#post104924

systick_millis_count is already volatile, doing it twice is not needed.

thank you, duff !