package/uclibc: use the generic help rules

package/uclibc: use the generic help rules

Note that the uclibc-menuconfig rule was guarded behind
BR2_TOOLCHAIN_BUILDROOT, which is wrong since we can build
glibc or musl toolchains too...

This is de facto fixed by moving the help text to the uClibc package.

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Arnout Vandecappelle <arnout@mind.be>
Cc: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
[Thomas: don't use the helper.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>