target/arm: fixup some of the commentary for arm-semi

This cleans up a number of the block comments to fit the proper style.
While we are at it we also reference the official specification and
document what the return register value can be.

Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
1 file changed