The code in thunk_64.S and thunk_32.S are exactly the same except for
the comments. Merge them in to thunk.S.

And since thunk_32.S was originated from thunk_64.S, the new merged
thunk.S is actually renamed from thunk_64.S.
Signed-off-by: Lai Jiangshan <jiangshan.ljs@antgroup.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Link: https://lore.kernel.org/r/20240407090558.3395-9-jiangshanlai@gmail.com