powerpc: udbg based backend for hvc_console

[Paul Mackerras]

David Gibson writes:

> This patch adds a new backend for the hvc console based on the
> low-level udbg callbacks.  This effectively implements a working
> runtime console in terms of the simple udbg primitives.  This is kind
> of a hack - since udbg isn't something you really want to be using
> routinely - but it's really useful during bringup.
> 
> This can be used to quickly implement a userspace usable console while
> you're working on a proper driver for whatever console I/O device the
> hardware has.  Or, it can be used to avoid writing a full blown
> tty/console driver entirely for quick-and-dirty I/O hardware that will
> later be replaced by something else.

Since only powerpc has udbg, shouldn't the Kconfig option depend on
PPC?

Paul.