ARM: dts: Update mem_dump node names for SM6150 and SM8150

mem_dump nodes are registered with minidump table, which has
restriction for region name length to be less than 12 chars.

So update mem_dump node names to add them successfully to minidump table.

Change-Id: Ie666d27212737ef40d47628d6d48a76149fb5477
Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>