Provide a minimal Console Terminal Block in the HWRPB.

Provide a minimal Console Terminal Block in the HWRPB so that operating
systems that depend on it can correctly initialize the console device.
This is suffucient, at least, for the BSD operating systems, but may not
be sufficient for Digital UNIX.

In addition to defining and filling out the structures, there are a couple
of other key changes:

- Redefine the a2 register passed by Qemu at start-up to also include
  some configuration flags, in addition to the CPU count, and define
  a flag to mirror the "-nographics" option.

- We need to initialize the HWRPB *after* initializing VGA, so that
  we'll know if a VGA device is present and in which slot for filling
  out the CTB.

Signed-off-by: Jason Thorpe <thorpej@me.com>
Message-Id: <20210613210934.21143-2-thorpej@me.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>