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* Add libfdt.mk helper makefile
* Remove unused libfdt files
* Minor changes to fdt.h and libfdt.h to make them C99 compliant

Adapted from 754d78b1

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Change-Id: I0847f1c2e6e11f0c899b0b7ecc522c0ad7de210c
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>