Silicon/Hisilicon/D06: Modify GTDT timer flag

Add always on capibility to GTDT timer flag to fix SBSA 36 fail
issue:
36 : SYS Timer if PE Timer not ON
     PE Timers are not always-on.
     Failed on PE -    0 for Level=  3 : Result:  --FAIL-- 1

Contributed-under: TianoCore Contribution Agreement 1.1
Signed-off-by: Ming Huang <ming.huang@linaro.org>
Reviewed-by: Leif Lindholm <leif.lindholm@linaro.org>