Pitch fix for IO surfaces

Pitch fix for IO surfaces

On MacOS, a Surface constructor receiving the 'pitchPprovided'
parameter wasn't using it for the surface's external pitch,
which was causing an error when using the Image::getPitch()
function, which returns getExternalPitchB(). Image::getPitch()
is used within Image::loadImageData(), which is used by gl
functions like glTexImage2D() and glTexSubImage2D(). Both the
internal and external buffers now use the parameter to solve
this issue.

Bug b/19979104

Change-Id: I9762ed53b535ae9eb052f57ee1ceed8ee87cb29c
Reviewed-on: https://swiftshader-review.googlesource.com/18828
Tested-by: Alexis Hétu <sugoi@google.com>
Tested-by: Nicolas Capens <nicolascapens@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>