arm: cdef: Add special cased versions for pri_strength/sec_strength being zero

Before:
ARM32:                    Cortex A7      A8      A9     A53     A72     A73
cdef_filter_4x4_8bpc_neon:    964.6   599.5   707.9   601.2   465.1   405.2
cdef_filter_4x8_8bpc_neon:   1726.0  1066.2  1238.7  1041.7   798.6   725.3
cdef_filter_8x8_8bpc_neon:   2974.4  1671.8  1943.9  1806.1  1229.8  1242.1
ARM64:
cdef_filter_4x4_8bpc_neon:                            569.2   337.8   348.7
cdef_filter_4x8_8bpc_neon:                           1031.1   623.3   633.6
cdef_filter_8x8_8bpc_neon:                           1847.5  1097.7  1117.5

After:
ARM32:                    Cortex A7      A8      A9     A53     A72     A73
cdef_filter_4x4_8bpc_neon:    798.4   524.2   617.3   506.8   432.4   361.1
cdef_filter_4x8_8bpc_neon:   1394.7   910.4  1054.0   863.6   730.2   632.2
cdef_filter_8x8_8bpc_neon:   2364.6  1453.8  1675.1  1466.0  1086.4  1107.7
ARM64:
cdef_filter_4x4_8bpc_neon:                            461.7   303.1   308.6
cdef_filter_4x8_8bpc_neon:                            833.0   547.5   556.0
cdef_filter_8x8_8bpc_neon:                           1459.3   934.1   967.9
26 jobs for master in 9 minutes and 7 seconds (queued for 3 seconds)
Status Job ID Name Coverage
  Style
passed #350392
amd64 debian
style-check

00:00:21

 
  Build
passed #350393
amd64 debian
build-debian

00:00:38

passed #350401
debian aarch64
build-debian-aarch64

00:01:10

passed #350402
debian aarch64
build-debian-aarch64-clang-5

00:00:51

passed #350405
debian armv7
build-debian-armv7

00:01:53

passed #350406
debian armv7
build-debian-armv7-clang-5

00:01:16

passed #350408
docker ppc64le
build-debian-ppc64le

00:00:49

passed #350394
amd64 debian
build-debian-static

00:00:38

passed #350404
debian aarch64
build-debian-werror

00:00:34

passed #350395
amd64 debian
build-debian32

00:00:43

passed #350403
macos
build-macos

00:00:27

passed #350407
amd64 debian allowed to fail
build-ubuntu-snap

00:00:56

passed #350399
amd64 debian
build-win-arm32

00:00:30

passed #350400
amd64 debian
build-win-arm64

00:00:31

passed #350396
amd64 debian
build-win32

00:00:46

passed #350397
amd64 debian
build-win32-unaligned-stack

00:00:41

passed #350398
amd64 debian
build-win64

00:00:52

 
  Test
passed #350409
amd64 debian
test-debian

00:00:47

passed #350415
debian aarch64
test-debian-aarch64

00:02:09

passed #350417
debian armv7
test-debian-armv7-clang-5

00:02:28

passed #350411
amd64 debian
test-debian-asan

00:02:38

passed #350412
amd64 debian
test-debian-msan

00:01:21

passed #350416
docker ppc64le
test-debian-ppc64le

00:01:29

passed #350413
amd64 debian
test-debian-ubsan

00:01:33

passed #350410
amd64 debian
test-debian-unaligned-stack

00:00:46

passed #350414
amd64 debian
test-win64

00:01:03