[TVMC] micro, run: Disable micro support when USE_MICRO=OFF

[gromero]

Do not generate 'tvmc micro' subcommand and disable micro device option
in 'tvmc run' when TVM is built without support for microTVM, i.e. with
set(USE_MICRO OFF).

Otherwise tvmc will crash on importing any tvm.micro module / class. For instance:

gromero@amd:~/git/tvm/build$ tvmc -h 
Traceback (most recent call last):
  File "/home/gromero/git/tvm/python/tvm/micro/session.py", line 35, in <module>
    from .base import _rpc_connect
ImportError: cannot import name '_rpc_connect' from 'tvm.micro.base' (/home/gromero/git/tvm/python/tvm/micro/base.py)

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/usr/lib/python3.9/runpy.py", line 188, in _run_module_as_main
    mod_name, mod_spec, code = _get_module_details(mod_name, _Error)
  File "/usr/lib/python3.9/runpy.py", line 147, in _get_module_details
    return _get_module_details(pkg_main_name, error)
  File "/usr/lib/python3.9/runpy.py", line 111, in _get_module_details
    __import__(pkg_name)
  File "/home/gromero/git/tvm/python/tvm/driver/tvmc/__init__.py", line 22, in <module>
    from . import micro
  File "/home/gromero/git/tvm/python/tvm/driver/tvmc/micro.py", line 26, in <module>
    import tvm.micro.project as project
  File "/home/gromero/git/tvm/python/tvm/micro/__init__.py", line 28, in <module>
    from .session import (
  File "/home/gromero/git/tvm/python/tvm/micro/session.py", line 37, in <module>
    raise ImportError("micro tvm is not enabled. Set USE_MICRO to ON in config.cmake")
ImportError: micro tvm is not enabled. Set USE_MICRO to ON in config.cmake
gromero@amd:~/git/tvm/build$ 

For any user, which is bad specially for the ones not interested in using tvmc for micro targets.

[gromero]

cc @areusch @leandron @mehrdadh for reviews.

[leandron]

LGTM

[leandron]

So given @ZQPei agreement in #9619, let merge this one.

[leandron]

Thanks @gromero @ZQPei and @mehrdadh!