msm: Add support for uncached buffer logging

Add an API to print data to a small uncached buffer.
When a system reset occurs valuable data may still
be remaining in the cache (e.g. last printks) and this
data will probably be lost, giving an incomplete picture
of what the system was last doing. By logging useful
information to this uncached region (e.g. readl/writel,
last printk) a better picture of what the system was
last doing emerges.

Change-Id: I1f2c548059cb6bba8003f11fd1c54e7f789dfbae
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>