For most firmware packages we use a vendor- prefix to make it clear
who has provided the firmware. The firmware-rtl8723bt package is only
used for Pine64 devices and actually contains configs that are specific
to Pine64 hardware (e.g. rtl8723bs_config-pine64.bin).
Let's rename it to firmware-pine64-rtl8723bt to make this more clear.
Also cleanup the APKBUILD a bit and provide the LICENSE file in a -doc
subpackage so we can legally redistribute that firmware.
