Add GPIO control in U-Boot

[mariarti]

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The idea is that when U-Boot boots itself, it can set GPIO/S to 0/1 by taking values from the env. For example: On any board with different pins to power on SD cards from which you actually need to take or put files (which are not powered on now, if there are MOSFETs on the GPIO and different cameras), include for example a LED indicating the start of the U-Boot, or other similar things.

For example, create a variable GPIO and there write the numbers with their state separated by a separator or as Igor says: "as it is done in extras, so do it in autorun i.e. everything that is written there - execute at boot start"

[dimerr]

https://github.com/OpenIPC/u-boot-hi3516cv100/commit/7a09e4b220a862bbc6afd55b5ac705842bec68b6