ARM: 7521/1: Fix semihosting Kconfig text

It seems we were missing some text in the title for the
semihosting DEBUG_LL option. Add in the "/O" and fix up some
minor typos in the help text.

Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>
Acked-by: Nicolas Pitre <nicolas.pitre@linaro.org>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>