AP_RPM: Improve rpm logging #326

Job	Run time
build (stm32f7, chibios, 10)	3m 45s
build (stm32h7, chibios, 10)	3m 41s
build (fmuv2-plane, chibios, 10)	2m 4s
build (periph-build, chibios, 10)	3m 33s
build (iofirmware, chibios, 10)	1m 29s
build (CubeOrange-bootloader, chibios, 10)	52s
build (fmuv3-bootloader, chibios, 10)	50s
build (revo-bootloader, chibios, 10)	1m 10s
build (stm32h7-debug, chibios, 10)	2m 28s
build (fmuv3, chibios, 10)	5m 32s
build (revo-mini, chibios, 10)	4m 33s
build (MatekF405-Wing, chibios, 10)	4m 37s
build (CubeOrange-ODID, chibios, 10)	2m 30s
build (CubeRedPrimary-bootloader, chibios, 10)	53s
build (configure-all, chibios, 10)	10m 3s
build (build-options-defaults-test, chibios, 10)	7m 47s
build (signing, chibios, 10)	2m 56s
build (CubeOrange-PPP, chibios, 10)	2m 6s
build (SOHW, chibios, 10)	3m 25s
build (Pixhawk6X-PPPGW, chibios, 10)	1m 10s
build (new-check, chibios, 10)	4m 27s
	1h 9m 51s

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