iommu/exynos: Fix master clock management for inactive SYSMMU

If SYSMMU controller is not active, there is no point in enabling master's
clock just for doing the the of internal state. This patch moves enabling
that clock to the block which actually does the register access.

Signed-off-by: Marek Szyprowski <m.szyprowski@samsung.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>