When initializing the core clocks, stick external memory into self-refresh.
This gains us a few cool things:
- support suspend-to-RAM with Linux
- reprogram clocks automatically when doing "go" on u-boot.bin in RAM
- make sure settings are stable before flashing new version
- finally fully unify initialize startup code path between LDR/non-LDR
Signed-off-by: Mike Frysinger <vapier@gentoo.org>