Subzero assumes that stores and loads to/from stack memory can take an
immediate offset. This isn't true for sub-vector loads and stores. We
can just use regular full vector loads and stores instead.

Bug b/37496321

Change-Id: Iaffd60f8077a4c9d602665421f90a7288ab04050
Reviewed-on: https://swiftshader-review.googlesource.com/13008Reviewed-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>