A few numbers didn't match between the default value entered
in Context.cpp and the constants from Config.hpp. A few default
values were also erroneously larger than required. Constants were
centralized in Config.hpp to solve the issue.

Change-Id: I60e5d93c43ce61e125c261bdf07ce50e7130a296
Reviewed-on: https://swiftshader-review.googlesource.com/4742Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>