configure: don't apply -O2 if extra-cflags sets -O

If your trying to debug and want to force -O0 then don't allow the
configure script to try and set -O2. You can use --enable-debug but that
enables a lot more stuff by default.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
framebuffer.c: cosmetic clean-ups

This just fixes up the brace style to be consistent with both rows and
cols.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
monitor: add support for dynamic command tables

This adds the scaffolding for creating dynamic command tables. Once a
monitor is initialised with dynamic command tables we can then add
additional commands to the monitor on demand.

This has the additional benefit of not having to build architecture
specific console commands into all builds of QEMU.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>