Blackfin: put memory into self-refresh before/after programming clocks

Blackfin: put memory into self-refresh before/after programming clocks

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>