ARM: AMx3xx: Allow arch specific code to use early DM

Early system initialization is being done before initf_dm is being called
in U-Boot. Then system will fail to boot if any of the DM enabled driver
is being called in this system initialization code. So, rearrange the
code a bit so that DM enabled drivers can be called during early system
initialization. This is inspired by commit e850ed82 ("ARM: OMAP4+: Allow
arch specific code to use early DM")

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>