sw64: ftrace: fix function graph tracing support

Sunway inclusion
category: feature
bugzilla: https://gitee.com/openeuler/kernel/issues/I645S9



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Rewrite ftrace_graph_caller to support function graph tracing for
ftrace_regs_caller, ftrace_caller and _mcount. To enable function
graph tracing, the nop instruction at ftrace_graph_call is replaced
with "call $26, ($27)" instruction. To disable tracing, replace the
nop instruction back.

Signed-off-by: He Sheng <hesheng@wxiat.com>
Reviewed-by: Cui Wei <cuiwei@wxiat.com>
Signed-off-by: Gu Zitao <guzitao@wxiat.com>