libc/eglibc: Make eglibc 2.11 and 2.12 not experimental

I haven't noticed the usual experimental testers complain about eglibc
2.11 or 2.12 being unstable. So stop marking them as experimental.

Signed-off-by: Bryan Hundven <bryanhundven@gmail.com>

 # Alpha specific configuration file

 config ARCH_alpha

     select ARCH_SUPPORTS_32

     select ARCH_DEFAULT_32

     select ARCH_USE_MMU

     select ARCH_SUPPORT_CPU

     select ARCH_SUPPORT_TUNE

     help

       The Alpha architecture.