Support specifying buffer start offset for USB requests.

Deprecated existing API which only supported passing buffer
and length in favor of a new one that also supports passing
the start.

Being able to pass a start index is very important because
the kernel imposes size limits on how much data can be transferred
at a time so we often need to transmit large buffers in chunks.

Change-Id: I3484b5e68f1ece61d4645ea04be8ee6a3b79169d