add support for internal sd card adapter paths (/dev/mmcblk)
Created by: Matthew-Otto
When writing sd cards from a device with an internal sdcard reader/writer, the device will be listed as something like /dev/mmcblk0 instead of /dev/sd*. The partition numbers for these devices are prefixed with a "p". ex: /dev/mmcblk0p1. This PR adds support for those devices