r600: A number of deqp-gles fixes

• Fix texture buffer offset alignment Fixes deqp-gles31: functional.texture.texture_buffer.modify.bufferdata.offset_1_alignments functional.texture.texture_buffer.modify.bufferdata.offset_7_alignments
• Don't set an index_bias for indirect draw calls Fixes regressions with tests from dEQP-GLES31.functional.draw_indirect.random.* Fixes c6c532fa
• Don't advertise support for scaled int16 vertex formats Fixes dEQP-GLES2. functional.vertex_arrays.single_attribute.strides.buffer_0_32_short3_vec4_dynamic_draw_quads_1 functional.vertex_arrays.single_attribute.strides.buffer_0_32_short3_vec4_dynamic_draw_quads_256