The blitter now supports integer types. This means:
- It supports conversions to/from integer types from/to
  other already supported types.
- It supports integer to integer conversions without going
  to an intermediate float format.

Also added a Blitter::GetScale() function to avoid having
2 instances of the same switch statement in the code and
added the read/write utility functions. The final Blitter
code is not longer peppered with switch statements and is,
hopefully, easier to read that way.

Change-Id: I80de519aaaa768f8cedd98f97dc4414dda75bf54
Reviewed-on: https://swiftshader-review.googlesource.com/4113Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>