Added RGB10_A2 implementation in the Blitter and cases in
related Surface utility functions.

Change-Id: I2b1a9cdc1acc605085fb0f853741cc2f75bf1c9b
Reviewed-on: https://swiftshader-review.googlesource.com/4420Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>