csky: Add perf_arch_fetch_caller_regs support

In trace events as tracepoints context are not able to
be retrieve with task_pt_regs. Without arch caller regs
support the pt_regs context will be all zero, perf can
not parsing the callchain and resolving the symbols
correctly, some time will even get into deadlock
while handling the page fault, eg:

perf kmem —page record ls

Changelog
 - Add test case cmd in comment
 - Use regs_fp(regs) which is defined in abi/regdef.h

Signed-off-by: Mao Han <han_mao@c-sky.com>
Signed-off-by: Guo Ren <guoren@kernel.org>