Add support for module_verbose

Set module_verbose to control the printing of information
about loaded modules and kernel:

0 MODULE_VERBOSE_SILENT None
1 MODULE_VERBOSE_SIZE Pathname and size
2 MODULE_VERBOSE_TWIDDLE as for 1 but also twiddle for progress
3 MODULE_VERBOSE_FULL extra detail

When the loader is verifying modules we already have a
running indication of progress and module_verbose=0 makes sense.

Reviewed by: rpokala
Differential Revision: https://reviews.freebsd.org/D34245