Adding the missing pixel store
parameters needed to use some
tests. Added the UnpackInfo
structure to minimize function
signature changes while sending
all unpack parameters to
loadImageData().

Change-Id: I86b660697ae726f902923066a9defe6d3a88860f
Reviewed-on: https://swiftshader-review.googlesource.com/2943Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>