ARM: sunxi: allow building without reset controller

The sunxi reset controller code is only used with sun6i (a31).
After the platform has been split up into per-soc options, it's
now possible to build it without the reset controller code, so
the base platform init must not call into the reset driver
if that is turned off at compile time.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>