Note that no decoding functionality is added here.
This cl merely acknowledges textures of the ETC2, EAC
and ASTC format by handling their related enums in
SwiftShader, and the byte data is then allowed to be
passed down all the way to the Surface object, where
the decoding code will be added. Also note that this
cl does not add the extensions strings required for
ASTC support, so ASTC is still unsupported after this cl.

Change-Id: I1d8aed0fb64b0d4c72846e87410750d1e485c46b
Reviewed-on: https://swiftshader-review.googlesource.com/3938Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <capn@google.com>