ARM: gemini: Add missing register definitions for gemini timer

Add missing register defintions for the gemini clocksource
Also do some #define' cleanup to make the code more readable.

Signed-off-by: Hans Ulli Kroll <ulli.kroll@googlemail.com>
Reviewed-by: Linus Walleij <linus.walleij@linaro.org>
Signed-off-by: Olof Johansson <olof@lixom.net>