gm107/ir: avoid combining geometry shader stores at 0x60

gm107/ir: avoid combining geometry shader stores at 0x60

This corresponds to gl_PrimitiveID and gl_Layer. When both of these are
stored in a single AST.64 or AST.128 operation, then it appears as
though the whole store fails. Fixes the recently extended
glsl-1.50-transform-feedback-builtins piglit, and also
gtf30.GL3Tests.transform_feedback.transform_feedback_builtins.

The issue was reproduced on GM107 and GP108 but not GK208 nor GK104.

Signed-off-by: Ilia Mirkin <imirkin@alum.mit.edu>