infra: Introduce BR2_HOST_NEEDS_JAVA

XBMC needs Java on the host in order to build, because it  uses a
code-generator which is build in two phases:
In the first phase SWIG is used to parse C++ header files that define the API.
SWIG outputs an XML file that contains a complete description of the structure
of the API.
In the second phase, the XML file is ingested by a Groovy (Java) program that
then creates C++ code that forms the bridge to the scripting language (Python).

The second phase is why we need java on the host.

You can learn more at the XBMC's wiki:
http://wiki.xbmc.org/index.php?title=Codegeneration#How_it_works

In order to check that, this patch introduce this mechanism in
dependencies.sh
It also defines the variable in Config.in

Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
---
Changes v6 -> v7:
  - Fixes old use of BUILDROOT_CONFIG instead of BR2_CONFIG
  - Add definition of the variable to Config.in
Changes v5 -> v6:
  - Remove useless loop (Thomas Petazzoni)
  - Thanks to Martin Bark idea, change this patch to have a non package
    specific variable.
Changes v1 -> v5:
  - Patch non existant before
xbmc: new package

XBMC is an award-winning free and open source (GPL) software media player and
entertainment hub for digital media.
This package was originally found at : https://github.com/huceke/buildroot-rbp
By gimli <ebsi4711@gmail.com>

Signed-off-by: Maxime Hadjinlian <maxime.hadjinlian@gmail.com>
Cc: gimli <ebsi4711@gmail.com>
---
Changes v6 -> v7:
  - None
Changes v5 -> v6:
  - Fix missing depends on OpenGL (Yann E. Morin)
  - Remove LIBCEC_RBP Config option (Yann E. Morin)
  - Fix dependency that were, in the end, not optionnal (Martin Bark)
  - Fix OpenGL check (Martin Bark)
  - Uses BR2_HOST_NEEDS_JAVA (Martin Bark)
Changes v4 -> v5:
  - Remove MAKE1, seems to work fine with parallel build.
Changes v3 -> v4:
  - Rework init script
  - Add systemd startup service
Changes v2 -> v3:
  - Fix indent
  - Change librtmp to rtmpdump
Changes v1 -> v2:
  - Fix header (Yann E. Morin)
  - Fix comment on toolchain option (Peter Korsgaard)