libc: Cleanup FreeBSD files ...

Remove code specific to FreeBSD so that they can be used in this
repository.

Change-Id: I5c11eb5b3c05a7fb91aed08371a1f7a0e6122a94
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

libc: Import files from FreeBSD ...

From commit aafd1cf:

- sys/sys/endian.h
- sys/arm/include/endian.h
- sys/arm64/include/endian.h
- sys/sys/errno.h
- lib/libc/strchr.c
- lib/libc/strcmp.c
- lib/libc/strncmp.c
- lib/libc/strnlen.c

strcasecmp() hasn't been imported.

Change-Id: I8a0787aec9ba8960a008fb5c66f7a73c84919b93
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

libc: Remove non-Arm files ...

Remove all files that don't have only Arm copyright. This is the first
step to cleanup the C library in this repository. They will be re-added
in the following patches.

Change-Id: I72c40a1620d1df3228fc397ec695d569a20245fd
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

Create a library file for libc ...

TF Makefile was linking all the objects files generated for the
c library instead of creating a static library that could be
used in the linking stage.

Change-Id: I721daea097e9b13cbb42c9f8eaa2af8fea0799cf
Signed-off-by: Roberto Vargas <roberto.vargas@arm.com>