To allow the USB to work in cases where there is a lot of filesystem
access, in particular on boot.
For example, registering of the USB CDC interface may fail if:
- the board file system is lfs2 (default), and
- sys.path contains entries for the local file system (default), and
- files are imported by boot.py or main.py from frozen bytecode of the file
system (common) and the file system contains many files, like 100.
In that case the board is very busy with scanning LFS, and registering the
USB interface seems to time out. This commit fixes this by allowing the
USB to make progress during filesystem reads.
Also switch existing MICROPY_EVENT_POLL_HOOK uses in this file to
MICROPY_EVENT_POLL_HOOK_FAST now that the latter macro exists.
5890a17ae0