doc: Remove experimental tag for SMC cache.

doc: Remove experimental tag for SMC cache.

SMC cache was introduced in 2.10 with experimental tag.
SMC cache is a layer of software cache located after EMC
cache. The purpose is to improve the performance of use
cases that many flows missing the EMC cache.

One can enable SMC cache using smc-enable=true option.

Signed-off-by: Yipeng Wang <yipeng1.wang@intel.com>
Acked-by: Ilya Maximets <i.maximets@samsung.com>
Signed-off-by: Ian Stokes <ian.stokes@intel.com>