package/uboot-tools: bump to version 2015.04

Bump to version 2015.04:
  * Enable optional support for FIT Signature Verification
  * Remove patch 0002-nostrip, it's upstream
  * Add musl patch
  * Add hash file

This patch supersedes "package/uboot-tools: bump to version 2015.01"
http://patchwork.ozlabs.org/patch/440396/



[Thomas:
  - Rewrap Config.in help text.
  - Move the paragraph about potential license compatibility issue
    from Config.in.host to Config.in, since it's really on the target
    package that such issues can be a problem.
  - Use += instead of = when adding the dependency on openssl, so that
    if other dependencies get added later, we don't overwrite them
    mistakenly.]

Signed-off-by: Jörg Krause <joerg.krause@embedded.rocks>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>