Change in coreboot[master]: mainboard/google/zoombini: move gpio.c into variants/zoombini

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Change subject: mainboard/google/zoombini: move gpio.c into variants/zoombini
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Patch Set 1: Verified+1

Build Successful

https://qa.coreboot.org/job/coreboot-checkpatch/19828/ : SUCCESS

https://qa.coreboot.org/job/coreboot-gerrit/65077/ : SUCCESS