linux-user: Fix coding style nits in qemu.h

We're about to move a lot of the code in qemu.h out into different
header files; fix the coding style nits first so that checkpatch
is happy with the pure code-movement patches. This is mostly
block-comment style but also a few whitespace issues.

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20210908154405.15417-2-peter.maydell@linaro.org>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>