squeezelite: new package

[Thomas:
  - replicate the ffmpeg "depends on" related to the broken NIOS2
    toolchains to the BR2_PACKAGE_SQUEEZELITE_FFMPEG option.
  - use the github helper function.
  - add hash file.]

Signed-off-by: Hiroshi Kawashima <kei-k@ca2.so-net.ne.jp>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>