main/postmarketos-initramfs: add missing USB gadget modules

init_functions.sh makes use of the mass_storage and acm USB gadget functions for error reporting, but the necessary kernel modules are not included in the initramfs at the moment. Because of this, the functionality works only on kernels where all these USB gadget functions are built-in and not built as modules.

Add the missing modules and fix the sort order while at it.