trusty: rpmb_dev: Use socket from init and update init script

Stop creating a socket on a persistent filesystem and use a socket
created by init in /dev/socket/ instead.

Many init script changes to make rpmb_dev.rc usable on cuttlefish.

Test: Build and run aosp_cf_x86_64_phone_trusty_vm-trunk_staging-userdebug
Bug: 309007107
Change-Id: Idc830211b3298d25bbb310dcb7489dd89fe5afc6