qcom_gcc: migrate the MSM8916 support to qcom_gcc
- migrate the MSM8916 (snapdragon 410) support to qcom_gcc
- add the full qcom_gcc / qcom_clk list to files.arm64, replacing the MSM8916 stub in sys/arm64/qualcomm .
Differential Revision: https://reviews.freebsd.org/D49706