libfdt: move headers to <linux/libfdt.h> and <linux/libfdt_env.h>

Thomas reported U-Boot failed to build host tools if libfdt-devel
package is installed because tools include libfdt headers from
/usr/include/ instead of using internal ones.

This commit moves the header code:
  include/libfdt.h         -> include/linux/libfdt.h
  include/libfdt_env.h     -> include/linux/libfdt_env.h

and replaces include directives:
  #include <libfdt.h>      -> #include <linux/libfdt.h>
  #include <libfdt_env.h>  -> #include <linux/libfdt_env.h>

Reported-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
diff --git a/board/phytec/pcm058/pcm058.c b/board/phytec/pcm058/pcm058.c
index 1538158..277590f 100644
--- a/board/phytec/pcm058/pcm058.c
+++ b/board/phytec/pcm058/pcm058.c
@@ -397,7 +397,7 @@
 
 #ifdef CONFIG_SPL_BUILD
 #include <spl.h>
-#include <libfdt.h>
+#include <linux/libfdt.h>
 
 static const struct mx6dq_iomux_ddr_regs mx6_ddr_ioregs = {
 	.dram_sdclk_0 = 0x00000030,
diff --git a/board/phytec/pfla02/pfla02.c b/board/phytec/pfla02/pfla02.c
index 136f1d5..18ff9ef 100644
--- a/board/phytec/pfla02/pfla02.c
+++ b/board/phytec/pfla02/pfla02.c
@@ -400,7 +400,7 @@
 #ifdef CONFIG_SPL_BUILD
 #include <asm/arch/mx6-ddr.h>
 #include <spl.h>
-#include <libfdt.h>
+#include <linux/libfdt.h>
 
 #define MX6_PHYFLEX_ERR006282	IMX_GPIO_NR(2, 11)
 static void phyflex_err006282_workaround(void)