selftests/bpf: Add a movsx selftest for sign-extension of R10

A movsx selftest is added for sign-extension of frame pointer R10.
The verification fails for both privileged and unprivileged
prog runs.

Signed-off-by: Yonghong Song <yonghong.song@linux.dev>
Link: https://lore.kernel.org/r/20230807175726.672394-1-yonghong.song@linux.dev


Signed-off-by: Martin KaFai Lau <martin.lau@kernel.org>