Set allow list for generic ramdisk

Devices that uses generic ramdisk must inherit from generic_ramdisk.mk.
This makefile ensures that only a set of files can be installed to the
ramdisk. Other files must be installed to the vendor-ramdisk.

Let aosp_arm64 use this makefile.

Fixes: 173742069
Test: manual
Change-Id: Ib2a4a208deaf2f4d707bec256207b4b8479a601a
(cherry picked from commit bc9608c4c3f3cd0ac3f29863209c80fcfe4e2f7f)