i965: Fix blorp clear of layered framebuffers.

From section 4.4.7 (Layered Framebuffers) of the GLSL 3.2 spec:

    When the Clear or ClearBuffer* commands are used to clear a
    layered framebuffer attachment, all layers of the attachment are
    cleared.

This patch fixes the blorp clear path for color buffers.

Fixes piglit test "spec/!OpenGL 3.2/layered-rendering/clear-color".
i965: Fix fast clear of depth buffers.

From section 4.4.7 (Layered Framebuffers) of the GLSL 3.2 spec:

    When the Clear or ClearBuffer* commands are used to clear a
    layered framebuffer attachment, all layers of the attachment are
    cleared.

This patch fixes the fast depth clear path.

Fixes piglit test "spec/!OpenGL 3.2/layered-rendering/clear-depth".
!UPSTREAM: main: check texture target when validating layered framebuffers.

From section 4.4.4 (Framebuffer Completeness) of the GL 3.2 spec:

    If any framebuffer attachment is layered, all populated
    attachments must be layered. Additionally, all populated color
    attachments must be from textures of the same target.

We weren't checking that the attachments were from textures of the
same target.

TODO:
- Make a piglit test for this, and validate it on Nvidia.