package/libpng: fix arm soft-float build

Bumping libpng to 1.6.44 with buildroot commit
583bb434ffe1eec0dbf6887dd719c3f41a6253e9
causes a build failure on arm because the NEON code is only available
for softfp and hardfp ABIs, and not soft-float.

Fixes:
http://autobuild.buildroot.net/results/021/02158525203d8c7f16a4a32637d44d6c87b7f333/

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Co-authored-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>
(cherry picked from commit a100286aa1eff05db57230eceebbb6aa79c63d1a)
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/libpng/libpng.mk

@@ -17,7 +17,9 @@ HOST_LIBPNG_DEPENDENCIES = host-pkgconf host-zlib
 LIBPNG_CONFIG_SCRIPTS = libpng$(LIBPNG_SERIES)-config libpng-config
 LIBPNG_CONF_OPTS = --disable-tools
 
-ifeq ($(BR2_ARM_CPU_HAS_NEON)$(BR2_aarch64),y)
+ifeq ($(BR2_aarch64),y)
+LIBPNG_CONF_OPTS += --enable-arm-neon
+else ifeq ($(BR2_ARM_CPU_HAS_NEON):$(BR2_ARM_SOFT_FLOAT),y:)
 LIBPNG_CONF_OPTS += --enable-arm-neon
 else
 LIBPNG_CONF_OPTS += --disable-arm-neon