Implement generic support for early printf. Thought I can't find the
paper trail now, this patch is similar to one posted for one of the
preliminary versions of a new armv6 port. I took them and made them
more generic. Option not enabled by default since each board/port has
to provide its own eputc, and possibly do other things as well...
Add support for mapping a small range of the SoC devices for debugging
purposes early in boot.