FROMLIST: pstore/ram: Rework logic for detecting ramoops reserved memory region

The reserved memory region for ramoops is assumed to be at a fixed
and known location when read from the devicetree. This is not desirable
in environments where it is preferred for the region to be dynamically
allocated at runtime, as opposed to it being fixed at compile time.

Change the logic for detecting the start and size of the ramoops
memory region by looking up the reserved memory region instead of
using platform_get_resource(), which assumes that the location
of the memory is known ahead of time.

Bug: 191636717
Link: https://lore.kernel.org/patchwork/patch/1451704/


Change-Id: I24066de9f4fe1f1575cb1bbb1687c37a2b1938a4
Signed-off-by: Isaac J. Manjarres <isaacm@codeaurora.org>
Signed-off-by: Mukesh Ojha <mojha@codeaurora.org>
Signed-off-by: Prasad Sodagudi <psodagud@codeaurora.org>
(cherry picked from commit bd2ca0ba)