ANDROID: GKI: drivers: of: Add API to find ddr device type

Add API to find the ddr device type from memory node.

Test: build
Bug: 150980314
Change-Id: I1cfc38d46f1ea0abc6fbe8cbb6e37cde72b9fc2e
Signed-off-by: Channagoud Kadabi <ckadabi@codeaurora.org>
(cherry picked from commit 368f22bc)
[hridya: added an EXPORT_SYMBOL_GPL statement to make the new
symbol avaialable to kernel modules].
Signed-off-by: Hridya Valsaraju <hridya@google.com>