msm: 8974: Add function to reserve memory from device tree

Memory reservations for memory pools or using memblock remove
must happen early at bootup. Add a function at early boot to
walk the flattened device tree and extract memory reservation
information from appropriate bindings in device tree. To ensure
that the memory is only reserved when a driver is enabled,
drivers must put EXPORT_COMPAT(<compat string>) in the driver
as well as adding the binding to the device tree. More
documentation is available in
Documentation/devicetree/bindings/arm/msm/memory-reserve.txt

Change-Id: I28fa71d7a30cea9af5447acb5d2dde562fa0f6de
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>