arch: arm64: enhance backtrace dump check

Examine the FP and LR values of each frame to prevent nested
exceptions caused by data aborts. Sometimes, abnormal FP and LR
values are not mapped by the MMU. If we access memory addresses
based on FP or LR values, a CPU data abort will occur. This issue
often accompanies stack overflow occurrences.

Based on this, it is safe to check the validity of memory mapping
with FP and LR values before accessing them.

Signed-off-by: Jungo Lin <jungolin.tw@gmail.com>