Silicon/Qemu/Sbsa: Enable Always-On capability for PE timers

Setting the Always-on Capability bit in GTDT table for
system PE timers in sbsa platform.This is also required
for ACS sbsa level 3 test compliancy.

Cc: Leif Lindholm <leif@nuviainc.com>
Cc: Ard Biesheuvel <ard.biesheuvel@arm.com>
Cc: Graeme Gregory <graeme@nuviainc.com>
Signed-off-by: Shashi Mallela <shashi.mallela@linaro.org>

[fixed compilation error]

Signed-off-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
Tested-by: Marcin Juszkiewicz <marcin.juszkiewicz@linaro.org>
Acked-by: Leif Lindholm <leif@nuviainc.com>