powerpc: Do not compile any dts if CONFIG_OF_ALL_DTBS=y

hulk inclusion
category:bugfix
bugzilla:50795
CVE:NA

-------------------

There are many warning when make the dts of powerpc.
And those dts would not be used.
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Acked-by: NXie XiuQi <xiexiuqi@huawei.com>
Signed-off-by: NChen Jun <chenjun102@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

arch/powerpc/boot/dts/Makefile

 # SPDX-License-Identifier: GPL-2.0
 
-subdir-y += fsl
+# subdir-y += fsl
 
 dtstree		:= $(srctree)/$(src)
-dtb-$(CONFIG_OF_ALL_DTBS) := $(patsubst $(dtstree)/%.dts,%.dtb, $(wildcard $(dtstree)/*.dts))
+# dtb-$(CONFIG_OF_ALL_DTBS) := $(patsubst $(dtstree)/%.dts,%.dtb, $(wildcard $(dtstree)/*.dts))