Define ICACHE_DISABLE/DCACHE_DISABLE to keep with upstream merge

Upstream got a change that defines L1_ENABLE when {I,D}CACHE_ENABLE is
defined, which they are by default.  It also define-gates some of the
ibuffer code with L1_ENABLE which breaks the sim.  Explicitly defining
these flags prevent this from happening.

radiance.mk

@@ -18,6 +18,7 @@ EXTRA_SIM_PREPROC_DEFINES += \
 	+define+LSU_DUP_DISABLE \
 	+define+DBG_TRACE_CORE_PIPELINE_VCS \
 	+define+PERF_ENABLE \
+	+define+ICACHE_DISABLE +define+DCACHE_DISABLE \
 	+define+NUM_THREADS=8 +define+NUM_WARPS=8
 
 # cargo handles building of Rust files all on its own, so make this a PHONY