gst1-plugins-base: re-enable the NEON audio resampler on 32-bit ARM

gst1-plugins-base: re-enable the NEON audio resampler on 32-bit ARM

The NEON audio resampler has been compiled out of every 32-bit ARM build
since 1.28. Its inline asm advances pointers with add.w, a Thumb-2 only
mnemonic that gas rejects in ARM (A32) state, which is how OpenWrt builds
ARM. The same add.w sits in the meson probe that gates HAVE_ARM_NEON, so
the probe fails first and hides the broken asm behind the generic C path.

Backport the upstream fix, which selects the operand form per ISA and
drops add.w from the probe. Thumb-2 code generation is unchanged.

Signed-off-by: Alexandru Ardelean <redacted>