added USB_MTPDISK_DUAL_SERIAL and USB_MTPDISK_TRIPLE_SERIAL

[caleb]

Hi, I was in need of MTPDISK with dual and triple serial.

I have created two PRs

Ccrome/add mtp dual serial and mtp triple serial by ccrome · Pull Request #789 · PaulStoffregen/cores

This patch adds support for USB_MTPDISK_DUAL_SERIAL and USB_MTPDISK_TRIPLE_SERIAL and is a companion to platformio/platform-teensy#119

github.com

added USB_MTPDISK_DUAL_SERIAL and USB_MTPDISK_TRIPLE_SERIAL by ccrome · Pull Request #119 · platformio/platform-teensy

This patch adds support for USB_MTPDISK_DUAL_SERIAL and USB_MTPDISK_TRIPLE_SERIAL and is a companion to PaulStoffregen/cores#789.

github.com

Is there anything else I need to do?