uclibc: move configuration options into the package

In preparation for the introduction of the eglibc library to the
internal toolchain backend, the options that allow to enable/disable C
library features such as largefile, IPv6, RPC and so on now belong to
the uClibc package.

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>