stmhal: Change calls to pfenv_printf to pfenv_vprintf.

Fixes printing bugs introduced by
cb66f41ebc4980f4e6b7543bece19e3b9daac25c.
stmhal: Fix REPL printing by cooking output sent to stdout_obj.

Recent changes to builtin print meant that print was printing to the
mp_sys_stdout_obj, which was sending data raw to the USB CDC device.
The data should be cooked so that \n turns into \r\n.