backtrace: Add backtrace for riscv. [1/2]

PD#SWPL-69248

Problem:
riscv need backtrace function.

Solution:
add backtrace for riscv.

Verify:
N/A

Change-Id: I62b7c871101bef37775971c3791c5c6039931d49
Signed-off-by: shijie.xiong <shijie.xiong@amlogic.com>
1 file changed