AP_EFI: fixed build on boards without EFI support #384

Job	Run time
build (stm32f7, chibios, 6)	22m 30s
build (stm32f7, chibios, 10)	24m 54s
build (stm32h7, chibios, 6)	17m 2s
build (stm32h7, chibios, 10)	16m 56s
build (fmuv2-plane, chibios, 10)	8m 23s
build (periph-build, chibios, 10)	24m 39s
build (iofirmware, chibios, 6)	1m 16s
build (iofirmware, chibios, 10)	1m 31s
build (CubeOrange-bootloader, chibios, 6)	1m 27s
build (CubeOrange-bootloader, chibios, 10)	1m 11s
build (revo-bootloader, chibios, 6)	1m 5s
build (revo-bootloader, chibios, 10)	1m 27s
build (stm32h7-debug, chibios, 6)	4m 34s
build (stm32h7-debug, chibios, 10)	5m 1s
build (fmuv3, chibios, 6)	10m 51s
build (fmuv3, chibios, 10)	11m 31s
build (revo-mini, chibios, 10)	20m 10s
build (MatekF405-Wing, chibios, 10)	16m 38s
build (CubeOrange-ODID, chibios, 10)	5m 43s
build (configure-all, chibios, 6)	9m 55s
build (configure-all, chibios, 10)	9m 24s
build (build-options-defaults-test, chibios, 6)	3m 25s
build (build-options-defaults-test, chibios, 10)	2m 56s
build (signing, chibios, 10)	15m 2s
build (stm32h7, chibios-py2)	18m 35s
	4h 16m 6s

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