gem5/gem5-aarch64-native: use oe-run-native

Persist gem5 binary in native sysroot. This allows executing the binary
with the standard oe-run-native script. We can also remove the wrapper
creation and the ".real" versioning, since paths are setup by oe-run-native.

Change-Id: I9fd46725c78e1a09a7142a9d343b140bb5a77088
Signed-off-by: Adrian Herrera <adrian.herrera@arm.com>
Signed-off-by: Jon Mason <jon.mason@arm.com>