pmbootstrap: add qcdt generation to the linux aportgen APKBUILDs
This checks the next box in #688 (closed) When the device has bootimg_qcdt set to true, the following is done to the linux APKBUILD:
- Add dtbtool to makedepends
- Call dtbTool during build() to generate dt.img
- Add the generated dt.img in the package's boot/dt.img