swupdate: allow luajit to enable HAVE_LUA

swupdate: allow luajit to enable HAVE_LUA

Until now, HAVE_LUA=y was only passed when BR2_PACKAGE_LUA=y. However,
swupdate can also use LuaJIT instead of the classic Lua. Therefore,
this commit updates the package to use BR2_PACKAGE_HAS_LUAINTERPRETER
and the luainterpreter virtual package.

Note that the swupdate configuration needs to be updated separately
(via swupdate-menuconfig) to enable Lua support, and to specify the
Lua version (which should be jit-5.1 to link against LuaJIT).

Signed-off-by: Jordan Yelloz <jordan@yelloz.me>
[Thomas: use the luainterpreter virtual package, expand commit log.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>