Currently, AM43xx just re-uses the version strings from AM33xx which is
wrong; the actual values for AM43xx are different. Fix this by adding
a separate version string array for AM43xx and use this instead.

Signed-off-by: Tero Kristo <t-kristo@ti.com>
Reported-by: Sekhar Nori <nsekhar@ti.com>
Reviewed-by: Lukasz Majewski <lukma@denx.de>
Reviewed-by: Tom Rini <trini@konsulko.com>