arm: add ARM-specific memory low-power support

Add ARM-specific memory low-power support and allow
the memory add code to call into platform-specific
code as the memory remove and low-power code does.

Change-Id: Ifb00366d8513092c8f14720980b4232fc8d758c0
Signed-off-by: Larry Bassel <lbassel@codeaurora.org>
(cherry picked from commit ae314e9efd9f24f6347342a765f923d560080059)