The cgroup_enable parameter is a Raspberry Pi kernel specific kernel
parameter. Upstream based kernel do not have the parameter, and hence
do not do anything.
This gets rid of the following message during boot:
Unknown kernel command line parameters "cgroup_enable=memory", will be passed to user space.
* Remove duplicate config.txt copy statement
* Use static cmdline.txt file
Instead of dynamically creating cmdline.txt use a static version of it.
This aligns with other boot loader/firmware configuration files and makes
it easier to customize the file per board.
