arm64: Dump memory surrounding PC, LR and SP registers only

Due to the verbosity of printing, dumping memory regions for all
register when many CPUs are online may contribute to flooded kernel
logs. Spinlock lockups due to the printing have also been seen to
result, compounding the problem due to additional prints.

Change-Id: I7440b2d77f03fd34f36816f549588fa89322ce5f
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>