A9 gtimer includes global control field and number of per-cpu fields.
But only per-cpu ones are migrated. This patch adds a subsection for
global control field migration.

Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
Message-id: 164422345976.2186660.1104517592452494510.stgit@pasha-ThinkPad-X280
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>