svga: return true for the PIPE_CAP_SM3 query

svga: return true for the PIPE_CAP_SM3 query

This just tells the state tracker to turn on the GL_ARB_shader_texture_lod
extension.  This simply allows the GLSL compiler to emit TXL and TXD
instructions for both vertex and fragment shaders.  We already support
these opcodes in the svga driver.  Though, the shadow2DGrad() Piglit
tests are failing.

Reviewed-by: José Fonseca <jfonseca@vmware.com>