of: clean-up unnecessary libfdt include paths

With the libfdt include fixups to use "" instead of <> in the
latest dtc import in commit 4760597 (scripts/dtc: Update to upstream
version 9d3649bd3be245c9), it is no longer necessary to add explicit
include paths to use libfdt. Remove these across the kernel.

Signed-off-by: Rob Herring <robh@kernel.org>
Acked-by: Ralf Baechle <ralf@linux-mips.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Cc: Paul Mackerras <paulus@samba.org>
Acked-by: Michael Ellerman <mpe@ellerman.id.au>
Acked-by: Grant Likely <grant.likely@linaro.org>
Cc: linux-mips@linux-mips.org
Cc: linuxppc-dev@lists.ozlabs.org

arch/powerpc/kernel/Makefile

@@ -2,7 +2,6 @@
 # Makefile for the linux kernel.
 #
 
-CFLAGS_prom.o		= -I$(src)/../../../scripts/dtc/libfdt
 CFLAGS_ptrace.o		+= -DUTS_MACHINE='"$(UTS_MACHINE)"'
 
 subdir-ccflags-$(CONFIG_PPC_WERROR) := -Werror