firmware oppo find 7a: add mechanism to retrieve firmware blobs from the android image/ partition if necessary

This patch adds a mechanism to retrieve firmware blobs form the android image/ partition if necessary using a openrc init script that creates a directory in /lib/firmware, mounts /dev/mmcblk0p1 there and copies over to /lib/firmware the binary blobs only if they do not exists there yet. Then /dev/mmcblk0p1 is unmounted. This mechanism allows for firmware blob updates through the package management system as the files are not touched if they exist, so newer blobs will not be downgraded (this has to be tested for eventual quirks).