bus: vexpress-config: Merge vexpress-syscfg into vexpress-config

The only thing that vexpress-syscfg does is provide a regmap to
vexpress-config bus child devices. There's little reason to have 2
components for this. The current structure with initcall ordering
requirements makes turning these components into modules more difficult.

So let's start to simplify things and merge vexpress-syscfg into
vexpress-config. There's no functional change in this commit and it's
still separate components until subsequent commits.

Cc: Lorenzo Pieralisi <lorenzo.pieralisi@arm.com>
Cc: Linus Walleij <linus.walleij@linaro.org>
Cc: Arnd Bergmann <arnd@arndb.de>
Reviewed-by: Sudeep Holla <sudeep.holla@arm.com>
Acked-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Acked-by: Liviu Dudau <liviu.dudau@arm.com>
Signed-off-by: Rob Herring <robh@kernel.org>