arm: fix atomic_testand{set,clear}_64 for ops on high bits

[rlibby]

Summary

The fix in bd03acedb804add1e22178d50eb2bfb703974ddf worked for 32-bit
ops, and for 64-bit ops for bit arguments of 0 - 95, but then was broken
for operations on the high 32 bits after that.

---

See also D27886, D27895, and bd03acedb804add1e22178d50eb2bfb703974ddf.

Test Plan

So far just buildkernel, I haven't been able to get qemu-system-arm working.

[mmel]

Ohh right, my next mistake. Seems I have not lucky day today :(
Thanks for fixing my stupid bugs.