ARM: OMAP: Move omap2_init_common_devices out of init_early

There's no need to call omap2_init_common_devices from init_early.

It no longer does anything else except reprogram the memory timings
for some boards, so it's better to do it later so we have a chance
to get console messages if something goes wrong.

Move it to happen after omap_serial_init gets called. And while
patching it anyways, rename it to omap_sdrc_init as suggested by
Benoit Cousson <b-cousson@ti.com>.

Signed-off-by: Tony Lindgren <tony@atomide.com>