arm: log readl/writel accesses

Log readl/writel accesses in the small uncached buffer.
readl/writel are typically used for reading from memory
mapped registers, which can cause hangs if accessed
unclocked. Log this information in a buffer to aid in
debugging.

Change-Id: Id72da6b028a3faf5d0d8e069e14d90e4671e3564
Signed-off-by: Laura Abbott <lauraa@codeaurora.org>