Move to micronucleus assembly for OSCCAL calibration

Some issues have been observed with OSCCAL calibration on older Dell
hosts. The micronucleus firmware enumerates correctly, but the Riso
clone then fails. Move to the assembly calibration code from
micronucleus to try and improve the situation.

Imported from https://github.com/micronucleus/micronucleus.git,
commit 7a53ce9e539a18fb46f7dc8e759f14833b10cc0c (July 31st 2016).