mstflint: make Python dependency optional

mstflint: make Python dependency optional

This commit adds a configuration symbol for the package
to make Python an optional dependency. If unselected,
Python packages won't be selected, and the Python-dependent
tools msftwreset, mstfwtrace, mstprivhost, mstresourcedump,
and mstresourceparse won't be included in the mstflint package.

Signed-off-by: Til Kaiser <mail@tk154.de>