uboot: fix build when libfdt-devel is installed system-wide

When libfdt-devel is installed system-wide, the build of U-Boot host
programs currently fails with lots of:

  HOSTCC  tools/aisimage.o
In file included from tools/../include/../lib/libfdt/libfdt.h:10:0,
                 from tools/../include/libfdt.h:1,
                 from tools/fdt_host.h:11,
                 from tools/imagetool.h:24,
                 from tools/aisimage.c:8:
/usr/include/libfdt_env.h:70:30: error: conflicting types for ‘fdt64_t’
 typedef uint64_t FDT_BITWISE fdt64_t;
                              ^~~~~~~
In file included from <command-line>:0:0:
././include/libfdt_env.h:19:16: note: previous declaration of ‘fdt64_t’ was here
 typedef __be64 fdt64_t;
                ^~~~~~~
In file included from ././include/libfdt_env.h:12:0,
                 from <command-line>:0:
/usr/include/libfdt_env.h:90:24: error: expected ‘)’ before ‘x’
 static inline uint32_t fdt32_to_cpu(fdt32_t x)
                        ^

This commit adds a fixup in the U-Boot code to fix this problem. The
fixup is equivalent to applying upstream commit
http://git.denx.de/?p=u-boot.git;a=commitdiff;h=e0d20dc1521e74b82dbd69be53a048847798a90a

,
but we can't use a patch for the uboot package, since people are using
arbitrary versions.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>