luaposix: fix runtime by selecting "bit32" instead of "bitop"

luaposix: fix runtime by selecting "bit32" instead of "bitop"

Since the bump of luaposix to 33.4.0, it doesn't work anymore at
runtime with LuaJIT or Lua 5.1. This can be tested with the following
defconfig:

BR2_x86_64=y
BR2_TOOLCHAIN_EXTERNAL=y
BR2_PACKAGE_LUA=y
BR2_PACKAGE_LUA_5_1=y
BR2_PACKAGE_LUAPOSIX=y

/usr/bin/lua: /usr/share/lua/5.1/posix/init.lua:17: module 'bit32' not found:
...

In older luaposix versions, it would try to load the 'bit' instead of
'bit32' module if LUAVER == 5.1. However, this feature was removed in
33.4.0.

So instead of adding a runtime dependency on luabitop, depend on
lua-bit32.

Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>