Deprecate the "pass an instruction opcode" flavor of cp15
access in favor of the "arm mcr ..." and "arm mrc ..."
commands, which offer fewer ways to break things.

Use the same EBNF syntax in the code as for the user's guide.

Update User's Guide to say where to find those magic values
(which table in the ARM920 TRM).

Signed-off-by: David Brownell <dbrownell@users.sourceforge.net>