luv: new package

libuv bindings for LuaJIT and Lua.

[Thomas:
  - Move the package to the sub-menu of Lua modules.
  - Remove no longer needed dependency on
    BR2_PACKAGE_HAS_LUAINTERPRETER.
  - Propagate dependencies of libuv (mmu, !static, threads)
  - Update to upstream version 1.7.4-4.
  - Add hash file.]

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