device-xiaomi-elish: Move from testing to community

Xiaomi Pad 5 Pro support is in good shape, it's time to move from testing to community.

Three packages are moved from testing to community:

1. device-xiaomi-elish
2. firmware-xiaomi-elish
3. linux-postmarketos-qcom-sm8250

Depends on MR: !5830 (merged)

PS:

firmware-xiaomi-elish's pkgrel version needs to be changed to 0 ( moving package is treated as newing package), otherwise ci will fail.