arm: Implement vceqq_p64, vceqz_p64 and vceqzq_p64 intrinsics
This patch adds implementations for vceqq_p64, vceqz_p64 and
vceqzq_p64 intrinsics.
vceqq_p64 uses the existing vceq_p64 after splitting the input vectors
into their high and low halves.
vceqz[q] simply call the vceq and vceqq with a second argument equal
to zero.
The added (executable) testcases make sure that the poly64x2_t
variants have results with one element of all zeroes (false) and the
other element with all bits set to one (true).