ARM: dts: keystone: Rename "msmram" node to "sram"

The device node name should reflect generic class of a device so rename
the "msmram" node and its children 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: Santosh Shilimkar <santosh.shilimkar@oracle.com>