soc: qcom: ramdump: Use cdev devices instead of misc devices

Misc devices are usually meant for really miscellaneous
devices that cannot 'fit' in any class. Since we have
quite a few subsystems requiring a ramdump nowadays,
let's move to using character devices directly.

Change-Id: I387fc4f3f59d61fab2ba89437bc3d3d6df24b69f
Signed-off-by: Vikram Mulukutla <markivx@codeaurora.org>
Signed-off-by: Kyle Yan <kyan@codeaurora.org>