ARM: dts: omap: Rename "ocmcram" node to "sram"

The device node name should reflect generic class of a device so rename
the "ocmcram" node to "sram".  This will be also in sync with upcoming DT
schema.  No functional change.

Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Tony Lindgren <tony@atomide.com>