mfd: vexpress: Define the device as MFD cells

This patch - finally, after over 6 months! :-( - addresses
Samuel's request to split the vexpress-sysreg driver into
smaller portions and define the device in a form of MFD
cells:

* LEDs code has been completely removed and replaced with
  "gpio-leds" nodes in the tree (referencing dedicated
  GPIO subnodes in sysreg - bindings documentation updated);
  this also better fits the reality as some variants of the
  motherboard don't have all the LEDs populated

* syscfg bridge code has been extracted into a separate
  driver (placed in drivers/misc for no better place)

* all the ID & MISC registers are defined as sysconf
  making them available for other drivers should they need
  to use them (and also to the user via /sys/kernel/debug/regmap
  which can be helpful in platform debugging)

Signed-off-by: Pawel Moll <pawel.moll@arm.com>
Acked-by: Lee Jones <lee.jones@linaro.org>
diff --git a/drivers/mfd/Kconfig b/drivers/mfd/Kconfig
index 3383412..490fd48 100644
--- a/drivers/mfd/Kconfig
+++ b/drivers/mfd/Kconfig
@@ -1227,12 +1227,17 @@
 
 endmenu
 
-config VEXPRESS_CONFIG
-	bool "ARM Versatile Express platform infrastructure"
-	depends on ARM || ARM64
+config MFD_VEXPRESS_SYSREG
+	bool "Versatile Express System Registers"
+	depends on VEXPRESS_CONFIG
+	default y
+	select CLKSRC_MMIO
+	select GPIO_GENERIC_PLATFORM
+	select MFD_CORE
+	select MFD_SYSCON
 	help
-	  Platform configuration infrastructure for the ARM Ltd.
-	  Versatile Express.
+	  System Registers are the platform configuration block
+	  on the ARM Ltd. Versatile Express board.
 
 endmenu
 endif