ARM: multi_v7_defconfig: Switch sunxi RSB driver from module to built-in

The sunxi RSB bus is used for peripherals like voltage regulators and
real-time clocks which should be available early in the boot process.
As a module, the driver will not be available until the root fs has been
mounted, so build the driver into the kernel.

Signed-off-by: Rask Ingemann Lambertsen <rask@formelder.dk>
Signed-off-by: Maxime Ripard <maxime.ripard@free-electrons.com>