There is multiple issues with the genaration of maintainer string

It uses DEBEMAIL and EMAIL enviroment variables, which may contain angle brackets,
creating invalid maintainer strings. The documented KBUILD_BUILD_USER and
KBUILD_BUILD_HOST variables are not used. Undocumented and uncommon NAME
variable is used. Refactor the Maintainer string to:

- use EMAIL or DEBEMAIL directly if they are in form "name <user@host>"
- use KBUILD_BUILD_USER and KBUILD_BUILD_HOST if set before falling
  back to autodetection
- no longer use NAME variable or the useless Anonymous string

The logic is switched from multiline if/then/fi statements to compact
shell variable substition commands.
Reported-by: NMathieu Malaterre <malat@debian.org>
Signed-off-by: NRiku Voipio <riku.voipio@linaro.org>
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>

Move debian/ directory generation out of builddeb to a new script,
mkdebian. The package build commands are kept in builddeb, which
is now an internal command called from debian/rules.

With these changes in place, we can now use dpkg-buildpackage from
deb-pkg and bindeb-pkg removing need for handrolled source/changes
generation.

This patch is based on the criticism of the current state of builddeb
discussed on:

https://patchwork.kernel.org/patch/9656403/Signed-off-by: NRiku Voipio <riku.voipio@linaro.org>
Signed-off-by: NMasahiro Yamada <yamada.masahiro@socionext.com>