virgl: add shader offset alignment to to v2 caps struct

virgl: add shader offset alignment to to v2 caps struct

This is the SSBO analogue to fe0647. User supplied data must
be a multiple of GL_SHADER_STORAGE_BUFFER_OFFSET_ALIGNMENT.

This fixes 44 GLES31 tests on airlied@'s GLES31 sketch branches with
Nvidia hardware, but this patch standalone can applied to master. The
alignment restriction on Nvidia is 32, hence the default value.

Example tests:
   dEQP-GLES31.functional.ssbo.layout.random.all_shared_buffer.0
   dEQP-GLES31.functional.ssbo.layout.multi_basic_types.single_buffer.std430

v2: Move to a better place in case statement
v3: Rebase

Reviewed-by: Dave Airlie <airlied@redhat.com>