Add integer vectors to GrSLType

BUG=skia:

Change-Id: I4a4a50e214f2240d83f6f0b02cf43e695c067933
Reviewed-on: https://skia-review.googlesource.com/8122
Reviewed-by: Brian Salomon <bsalomon@google.com>
Commit-Queue: Chris Dalton <csmartdalton@google.com>
6 files changed