From the documentation it is not clear what this SPI register is about.

Moreover, neither linux driver nor xvisor driver are using this SPI register.

For now we just remove it and issue a log on register write access.
Signed-off-by: NJean-Christophe Dubois <jcd@tribudubois.net>
Message-id: 20170107122047.26300-1-jcd@tribudubois.net
Reviewed-by: NPeter Maydell <peter.maydell@linaro.org>
Signed-off-by: NPeter Maydell <peter.maydell@linaro.org>