README: PMU: Optimize dts description #16

Job	Run time
kernel (zsb-64lp64, riscv64-unknown-linux-gnu-)	53s
kernel (opensbi-1.3-64lp64, riscv64-unknown-linux-gnu-)	44s
kernel (linux-6.6-64lp64, riscv64-unknown-linux-gnu-)	21m 57s
kernel (linux-6.6-64lp64-debug, riscv64-unknown-linux-gnu-)	36m 8s
kernel (linux-6.6-64ilp32, riscv64-unknown-elf-)	36m 18s
kernel (zsb-32ilp32, riscv32-unknown-linux-gnu-)	30s
kernel (opensbi-1.3-32ilp32, riscv32-unknown-linux-gnu-)	46s
kernel (linux-6.6-32ilp32, riscv32-unknown-linux-gnu-)	20m 12s
kernel (zsb-64lp64-xt, riscv64-unknown-linux-gnu-)	1m 2s
kernel (opensbi-0.9-64lp64, riscv64-unknown-linux-gnu-)	1m 7s
kernel (linux-5.10-64lp64, riscv64-unknown-linux-gnu-)	11m 36s
	2h 11m 13s

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