There are some bits in the code which were used to store the commandline for
the semihosting call. These bits are now write-only and can be removed.

Signed-off-by: Wolfgang Schildbach <wschi@dolby.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Riku Voipio <riku.voipio@iki.fi>