Add interface to remove address from fault filter ring by resetting
fault ring entry key, then future vm fault on the address will be
processed to recover.

Define fault key as atomic64_t type to use atomic read/set/cmpxchg key
to protect fault ring access by interrupt handler and interrupt deferred
work for vg20. Change fault->timestamp to 48-bit to share same uint64_t
with 8-bit fault->next, it is enough for 48bit IH timestamp.
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <Felix.Kuehling@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>