libopencore-amrnb: cosmetics: Group all encoder-related code together

CC: libav-stable@libav.org
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
(cherry picked from commit 81ae57a269782fbfc9e11548d1e6605f13d65c9b)
libopencore-amr: Conditionally compile decoder and encoder bits

CC: libav-stable@libav.org
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
(cherry picked from commit f6ad3ca159edcd2e48634bf39b9cd4a85af29cb1)
libopencore-amrwb: Make AMR-WB ifdeffery more precise

The library might provide an encoder in the future, so it's better to
check for the presence of the decoder rather than just the library.

CC: libav-stable@libav.org
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
(cherry picked from commit ed89cad6aa04bbd692b3eb21c0e0bb56aca77130)
build: The libopencore-amrnb encoder depends on audio_frame_queue

CC: libav-stable@libav.org
Signed-off-by: Luca Barbato <lu_zero@gentoo.org>
(cherry picked from commit d0fd1dd559b8362bdbca3405f739e0cc202d62e7)