Fixed loading GL_RGB10_A2UI texture format

Fixed loading GL_RGB10_A2UI texture format

The GL_RGB10_A2UI was being unpacked as a double sized version of
GL_UNSIGNED_SHORT_5_5_5_1, which it is not. The channels are not
stored in the same order for these 2 formats.

This fixes all "rgb10_a2ui" related test in:
dEQP-GLES3.functional.texture.format.sized.*
dEQP-GLES3.functional.texture.specification.*

Change-Id: I0d398d0537a440906e9ef3aeb01fe4e782f778b6
Reviewed-on: https://swiftshader-review.googlesource.com/11168
Tested-by: Alexis Hétu <sugoi@google.com>
Reviewed-by: Nicolas Capens <nicolascapens@google.com>