build: add avresample after avcodec to FFLIBS

avcodec might depend on avresample and with --as-needed required symbols
might be get removed if avresample is linked before avcodec.
Fixes link failures of avprobe and avplay on aarch64 with
--enable-neon-clobber-test.
configure: fix enable-libopus help string
aarch64: opus NEON iMDCT and FFT

Opus celt decoding 11% faster and the iMDCT over 2.5 times faster on
Apple's A7.
Merge commit '5e2ba41d4b94de1fa5267081d6c4b6b262c8d86f'

* commit '5e2ba41d4b94de1fa5267081d6c4b6b262c8d86f':
  build: add avresample after avcodec to FFLIBS

Conflicts:
	Makefile

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit '7c5ca546a0747a20c7f7fb5550455c3042699ee9'

* commit '7c5ca546a0747a20c7f7fb5550455c3042699ee9':
  configure: fix enable-libopus help string

See: 434ba17b22c61d968d595c02230c38e0bef1ea24
Merged-by: Michael Niedermayer <michaelni@gmx.at>
Merge commit 'd3f5b94762fb803c0f3b29f9ad6c5eaa813998ba'

* commit 'd3f5b94762fb803c0f3b29f9ad6c5eaa813998ba':
  aarch64: opus NEON iMDCT and FFT

Merged-by: Michael Niedermayer <michaelni@gmx.at>
Revert "avcodec/hevc: fix outputted AVFrame.key_frame"

This is not correct

Requested-by: mraulet
This reverts commit 973de9ebf8796bc2720a9959a9a535cf4023c58a.