MultiplyAddPairs is implemented using VMULL+VPADD.
MultiplyHighSigned/Unsigned is implemented using VMULL+VSHRN.
SubVectorLoad/Store is implemented using VLDR/VLD1/VSTR/VST1.
VectorPackSigned/Unsigned is implemented using two VQMOVN.

Bug b/37496078
Bug b/37496856
Bug b/37496321
Bug b/37496082

Change-Id: I141fd901d53da24ce780f503dc7ad17b94fc6ba8
Reviewed-on: https://chromium-review.googlesource.com/693049Reviewed-by: Jim Stichnoth <stichnot@chromium.org>
Reviewed-on: https://swiftshader-review.googlesource.com/12709Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>