EGL: default to HAL_DATASPACE_UNKNOWN.

The refactoring in ag/3926362 accidentally changed the dataspace used
when no colorspace is specified to HAL_DATASPACE_SRGB_LINEAR. Go back
to using HAL_DATASPACE_UNKNOWN in that case.

Bug: 79248854
Bug: 76088973
Test: Ran some dEQP tests on Pixel XL.
Change-Id: Ie723f8a0da71a2938e2af3b340a1660a976a071f