Builds of gs101 targets with pKVM force-enabled have an init service
which checks that /dev/kvm exists and if not, runs misc_writer to
instruct the bootloader to enable pKVM, and forces a reboot.
Assign the binary to the existing vendor_misc_writer domain and add
permission to execute the /vendor/bin/misc_writer binary. Since this is
for tests only, the rules are only added to targets that define
TARGET_PKVM_ENABLED.
Bug: 192819132
Test: flash a _pkvm build, observe double-reboot, check /dev/kvm exists
Change-Id: I5f9962e4cdd3ec267ab19ea4485e4e94a3ec15cd