AP_GPS: allow for EAHRS_SENSORS to not include GPS #32483

Job	Run time
build (chibios, Durandal)	19m 13s
build (chibios, MatekF405)	17m 10s
build (chibios, KakuteF7)	16m 17s
build (chibios, MatekH743-bdshot)	19m 48s
build (chibios, Pixhawk1-1M)	16m 58s
build (chibios, MatekF405-CAN)	4m 3s
build (chibios, DrotekP3Pro)	4m 27s
build (chibios, Hitec-Airspeed)	5m 8s
build (chibios, f103-GPS)	5m 44s
build (disco, armhf)	16m 6s
	2h 4m 54s

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