glsl/linker: Pass absolute location to add_shader_variable()

glsl/linker: Pass absolute location to add_shader_variable()

This lets us pass in the absolution location of a variable instead of
computing it in add_shader_variable() based on variable location and
bias. This is in preparation for recursing into struct variables.

Signed-off-by: Kristian Høgsberg Kristensen <kristian.h.kristensen@intel.com>
Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>