[PATCH] ucom console final patch

[Emmanuel Dreyfus <manu%netbsd.org@localhost>]

Hello

I think I am done with ucom console support. Here are the
changes: to EFI bootstrap, ucom driver, and documentation.
https://dl.espci.fr/ticket/890a80f4edf68d21b739a684427671aa

boot -a and DDB work, with some obvious limitations for the
later. I am not sure how how it copes with a panic while 
usb soft interrupt is in progress. 

There is a single anoying problem left: some DDB comand output
are fine, some other are garbled, I am not sure why. Example
of garbled output:
--db{4}>  bt 

            reakpoint() attnetbsd:breakpoint+0x5

com_cnlwp() attnetbsd:ucom_cnlwp+0x161

I plan to commit within a few days if there are no objections.


-- 
Emmanuel Dreyfus
manu%netbsd.org@localhost