hw/core: Add a config switch for the "register" device

The "register" device is only used by certain machines. Let's add
a proper config switch for it so that it only gets compiled when we
really need it.

Message-Id: <20190817101931.28386-5-thuth@redhat.com>
Reviewed-by: NPhilippe Mathieu-Daudé <philmd@redhat.com>
Reviewed-by: NAlistair Francis <alistair.francis@wdc.com>
Signed-off-by: NThomas Huth <thuth@redhat.com>

hw/Kconfig

@@ -76,3 +76,4 @@ config XILINX_AXI
 
 config XLNX_ZYNQMP
     bool
+    select REGISTER

hw/core/Kconfig

@@ -9,3 +9,6 @@ config FITLOADER
 
 config PLATFORM_BUS
     bool
+
+config REGISTER
+    bool

hw/core/Makefile.objs

@@ -17,7 +17,7 @@ common-obj-$(CONFIG_SOFTMMU) += machine.o
 common-obj-$(CONFIG_SOFTMMU) += loader.o
 common-obj-$(CONFIG_FITLOADER) += loader-fit.o
 common-obj-$(CONFIG_SOFTMMU) += qdev-properties-system.o
-common-obj-$(CONFIG_SOFTMMU) += register.o
+common-obj-$(CONFIG_REGISTER) += register.o
 common-obj-$(CONFIG_SOFTMMU) += or-irq.o
 common-obj-$(CONFIG_SOFTMMU) += split-irq.o
 common-obj-$(CONFIG_PLATFORM_BUS) += platform-bus.o

hw/dma/Kconfig

@@ -16,6 +16,7 @@ config I8257
 
 config ZYNQ_DEVCFG
     bool
+    select REGISTER
 
 config STP2000
     bool