ARM: AMx3xx: Centralize early clock initialization

This is similar to Commit 93e6253d ("ARM: OMAP4/5: Centralize
early clock initialization") that was done for OMAP4+, reflecting the same
for AM33xx and AM43xx SoCs to centralize clock initialization.

Signed-off-by: Lokesh Vutla <lokeshvutla@ti.com>
Reviewed-by: Tom Rini <trini@konsulko.com>
[trini: Add setup_early_clocks that calls setup_clocks_for_console for
        ti81xx]
Signed-off-by: Tom Rini <trini@konsulko.com>