add help docs to flashtool with groups and some new arg requirements
add help docs to flashtool with groups and some new arg requirements

Some other reorganization is still TODO, and also possibly remove
redundant options --noram and --reset, but I want to keep this CL
simple.

bug: 238690018

Change-Id: I7f90751b3410c9fade74447bacbd0a8e48a208a3
GitOrigin-RevId: b48243fd1e95232999bde45bfa35e7346394609f

google-coral/coralmicro,google-coral/coralmicro,google-coral/coralmicro,google-coral/coralmicro,google-coral/coralmicro