efivar: new package

efivar: new package

efivar contains tools and libraries to manipulate EFI variables.

This package has some restrictions to build. It needs uchar.h which
apparently does not come in uClibc, and it also needs
__bswap_constant_*() definitions which are only present in glibc.
So, this package was limited to build with glibc toolchains.

Although it probably makes sense mostly on x86, x86-64 and aarch64
architectures, there are no architecture specific limitations which
would prevent it to build for other architectures, so this restriction
was not imposed. This package has been build-tested additionaly on many
architectures which support glibc, such as mips, MicroBlaze, sparc64,
ppc64. There were some build flag issues found when building to some of
these some architectures, although the flags can be also added in the
general case, so they were added by default.

It has also been found that in some host systems it failed to build due
to not generating the .pc files. This has been tracked to the use of
make 3.81, so a patch was prepared for it and was submitted upstream.
There's also a dependency on the linux/nvme.h header, which is somewhat
conturbed, as it has appeared in user space linux headers 3.12 and in
4.4 it was renamed. This has been solved by restricting it to build with
linux headers >= 3.12 and a patch from upstream was picked which fixes
it for linux headers >= 4.4.

Signed-off-by: Erico Nunes <nunes.erico@gmail.com>
[Thomas:
 - Pass TARGET_LDFLAGS in LDFLAGS.
 - Pass -shared-libgcc only on Microblaze.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>