riscv: Add kprobes supported

This patch enables "kprobe & kretprobe" to work with ftrace
interface. It utilized software breakpoint as single-step
mechanism.

Some instructions which can't be single-step executed must be
simulated in kernel execution slot, such as: branch, jal, auipc,
la ...

Some instructions should be rejected for probing and we use a
blacklist to filter, such as: ecall, ebreak, ...

We use ebreak & c.ebreak to replace origin instruction and the
kprobe handler prepares an executable memory slot for out-of-line
execution with a copy of the original instruction being probed.
In execution slot we add ebreak behind original instruction to
simulate a single-setp mechanism.

The patch is based on packi's work [1] and csky's work [2].
 - The kprobes_trampoline.S is all from packi's patch
 - The single-step mechanism is new designed for riscv without hw
   single-step trap
 - The simulation codes are from csky
 - Frankly, all codes refer to other archs' implementation

 [1] https://lore.kernel.org/linux-riscv/[email protected]/
 [2] https://lore.kernel.org/linux-csky/[email protected]/

Signed-off-by: Guo Ren <[email protected]>
Co-developed-by: Patrick Stählin <[email protected]>
Signed-off-by: Patrick Stählin <[email protected]>
Acked-by: Masami Hiramatsu <[email protected]>
Tested-by: Zong Li <[email protected]>
Reviewed-by: Pekka Enberg <[email protected]>
Cc: Patrick Stählin <[email protected]>
Cc: Palmer Dabbelt <[email protected]>
Cc: Björn Töpel <[email protected]>
Signed-off-by: Palmer Dabbelt <[email protected]>

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