[lldb][Process/FreeBSDKernelCore] Add riscv64 support (#180670)
This is LLDB version of
https://cgit.freebsd.org/ports/tree/devel/gdb/files/kgdb/riscv-fbsd-kern.c.
This enables selecting riscv64 and reading registers from PCB structure
on core dump and live kenrel debugging while trapframe unwinding support
will be implemented in future. Test files using core dump from riscv64
will be implemented once other kernel debugging improvements are done.
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Signed-off-by: Minsoo Choo <minsoochoo0122@proton.me>