[COMMON] exynos/iommu: add suspended state

[COMMON] exynos/iommu: add suspended state

This patch added suspended state that becomes true when sysmmu goes to
suspend state. No SFR access is allowed if sysmmu is in suspended.

Without suspended state, some operation involving SFR access like tlb
invalidation would make external abort because it only checks internal
reference count before SFR access, and internal reference count is
remained after sysmmu becomes suspend state.

Change-Id: I7460e8b0b96de5f46584cc299dc2e659fc34da44
Signed-off-by: Janghyuck Kim <janghyuck.kim@samsung.com>