Use ARRAY_SIZE to calculate the number of altsettings

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>
Clean up Makefile

Make all the targets pertaining to the flashing of the
micorcontrollers be aware of the type of the microcontroller used.
This allows for separation of serial vs DFU mask-ROM bootloader
flashing commands.

Signed-off-by: Andrey Smirnov <andrew.smirnov@gmail.com>