scripts: re-enable some now fixed dtc warnings

We can re-enable some dtc warnings that have been completely or mostly
fixed. There are a few remaining ones in arm64 dts files which crept in
recently.
Signed-off-by: Rob Herring <robh@kernel.org>

scripts/Makefile.lib

@@ -276,10 +276,7 @@ DTC ?= $(objtree)/scripts/dtc/dtc
 # Disable noisy checks by default
 ifeq ($(findstring 1,$(KBUILD_ENABLE_EXTRA_GCC_CHECKS)),)
 DTC_FLAGS += -Wno-unit_address_vs_reg \
-	-Wno-simple_bus_reg \
 	-Wno-unit_address_format \
-	-Wno-pci_bridge \
-	-Wno-pci_device_bus_num \
 	-Wno-pci_device_reg
 endif