anv: Don't define has_slm in emit_l3_config for gen11+
For some gen12+ platforms, L3 config can be NULL leading to a seg-fault in emit_l3_config. But, we don't use has_slm for gen11+, so we can just avoid declaring the variable.
Ref: 633dec71 ("anv: Set L3 full way allocation at context init if L3 cfg is NULL")
Ref: !9534 (merged)
Fixes: 581e68bc ("anv: move L3 config emission to genX_state.c")
Cc: @llandwerlin