ARM: dts: exynos: Rename SysRAM node to "sram"

The device node name should reflect generic class of a device so rename
the SysRAM node from "sysram" to "sram".  The child nodes stay as before
as "smp-sysram" to match their real purpose.  This will be also in sync
with upcoming DT schema.  No functional change.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>