qcom: ssr: Add the err_fatal_gpio property to subsystem descriptor

Add and derive the err_fatal_gpio property for the subsystem
from the existing entry in DT.

CRs-Fixed: 746414
Change-Id: I20e587a0a3c4be923a126733a2300529f0120b06
Signed-off-by: Deepak Katragadda <dkatraga@codeaurora.org>