Purge xbus in BaseSubsystem #860

Job	Run time
jtag-dtm-test (freechips.rocketchip.system.WithJtagDTMSystem_freechips.rocketchip.system.DefaultC...	21m 41s
riscv-tests (DefaultConfig)	19m 25s
jtag-dtm-test (freechips.rocketchip.system.WithJtagDTMSystem_freechips.rocketchip.system.DefaultR...	20m 3s
emulator (DefaultSmallConfig)	12m 44s
riscv-arch-test	0s
riscv-tests (DefaultBufferlessConfig)	19m 35s
jtag-dtm-test (freechips.rocketchip.system.WithJtagDTMSystem_freechips.rocketchip.system.WithDebu...	17m 59s
emulator (DualBankConfig)	13m 28s
emulator (DualChannelConfig)	13m 27s
jtag-dtm-test (freechips.rocketchip.system.WithJtagDTMSystem_freechips.rocketchip.system.WithDebu...	17m 10s
riscv-tests (DefaultRV32Config)	19m 18s
emulator (DualChannelDualBankConfig)	13m 45s
riscv-tests (TinyConfig)	13m 33s
emulator (RoccExampleConfig)	12m 58s
riscv-tests (DefaultFP16Config)	14m 7s
emulator (Edge128BitConfig)	13m 33s
emulator (Edge32BitConfig)	13m 2s
emulator (QuadChannelBenchmarkConfig)	13m 32s
emulator (EightChannelConfig)	13m 41s
emulator (DualCoreConfig)	13m 21s
emulator (MemPortOnlyConfig)	13m 10s
emulator (MMIOPortOnlyConfig)	12m 55s
emulator (CloneTileConfig)	14m 46s
emulator (HypervisorConfig)	13m 25s
	5h 50m 38s

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