ARM: ep93xx: use soc bus

Use the soc bus to report the silicon revision and Maverick Key. Both
are not currently exposed to the user. In addition, fill in the SoC
family and machine for completeness.

Signed-off-by: H Hartley Sweeten <hsweeten@visionengravers.com>
Acked-by: Ryan Mallon <rmallon@gmail.com>
Signed-off-by: Ryan Mallon <rmallon@gmail.com>
Cc: Alexander Shiyan <shc_work@mail.ru>
Signed-off-by: Olof Johansson <olof@lixom.net>