Add rx-virt target specification document.
Signed-off-by: Yoshinori Sato <ysato@users.sourceforge.jp>
Message-Id: <20200308130637.37651-1-ysato@users.sourceforge.jp>
[PMD: Cover in MAINTAINERS, rename as gdbsim, use machine argument]
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
