Implement CI for hifive unmatched #228

Job	Run time
test-runtime-format	15s
build (generic, 32)	35m 47s
test-runtime-functionality	22s
build (generic, 64)	28m 48s
build (hifive_unmatched, 64)	31m 45s
build (cva6, 32)	24m 23s
build (cva6, 64)	27m 46s
build (mpfs, 64)	34m 11s
combine-caches	14m 10s
test-system-functionality / test-system (generic, 32)	1m 32s
test-runtime-build / build-runtime (generic, 32)	41s
test-system-functionality / test-system (generic, 64)	1m 41s
test-runtime-build / build-runtime (generic, 64)	29s
test-system-functionality / test-system (mpfs, 64)	6m 6s
test-runtime-build / build-runtime (hifive_unmatched, 64)	43s
test-system-functionality / test-system (cva6, 64)	15m 47s
test-runtime-build / build-runtime (cva6, 32)	27s
test-system-functionality / test-system (hifive_unmatched, 64)	8m 4s
test-runtime-build / build-runtime (cva6, 64)	26s
test-runtime-build / build-runtime (mpfs, 64)	37s
	3h 54m 0s

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