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: Mathieu Malaterre <malat@debian.org>
Signed-off-by: Riku Voipio <riku.voipio@linaro.org>
Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>