main, glsl: Add UniformDataDefaults which stores uniform defaults

main, glsl: Add UniformDataDefaults which stores uniform defaults

The ARB_get_program_binary extension requires that uniform values in a
program be restored to their initial value just after linking.

This patch saves off the initial values just after linking. When the
program is restored by glProgramBinary, we can use this to copy the
initial value of uniforms into UniformDataSlots.

V2 (Timothy Arceri):
 - Store UniformDataDefaults only when serializing GLSL as this
   is what we want for both disk cache and ARB_get_program_binary.
   This saves us having to come back later and reset the Uniforms
   on program binary restores.

Signed-off-by: Timothy Arceri <tarceri@itsqueeze.com>
Signed-off-by: Jordan Justen <jordan.l.justen@intel.com> (v1)
Reviewed-by: Tapani Pälli <tapani.palli@intel.com>