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

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.

Reviewed by: markj, mmel
Sponsored by: Dell EMC Isilon
Differential Revision: https://reviews.freebsd.org/D27897