ARM: vexpress: refine dependencies for new code

The versatile express changes for 3.16 introduced a number of
build regressions for randconfig kernels by not tracking dependencies
between the components right.

This patch tries to rectify that:

* the mach-vexpress code cannot link without the syscfg driver,
  which in turn needs MFD_VEXPRESS_SYSREG
* various drivers call devm_regmap_init_vexpress_config(), which
  has to be exported so it can be used by loadable modules
* the configuration bus uses OF DT helper functions that are not
  available to platforms disable CONFIG_OF
* The sysreg driver exports GPIOs through gpiolib, which can
  be disabled on some platforms.
* The clocksource code cannot be built on platforms that don't
  use modern timekeeping but rely on gettimeoffset.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/drivers/bus/vexpress-config.c b/drivers/bus/vexpress-config.c
index 27a07df..a64763b 100644
--- a/drivers/bus/vexpress-config.c
+++ b/drivers/bus/vexpress-config.c
@@ -118,7 +118,7 @@
 
 	return regmap;
 }
-
+EXPORT_SYMBOL_GPL(devm_regmap_init_vexpress_config);
 
 struct device *vexpress_config_bridge_register(struct device *parent,
 		struct vexpress_config_bridge_ops *ops, void *context)