png: add libpng port #350

Job	Run time
call-ci / build (armv7a7-imx6ull-evk)	4m 8s
call-ci / build (armv7a9-zynq7000-qemu)	1m 18s
call-ci / build (armv7a9-zynq7000-zedboard)	1m 31s
call-ci / build (armv7a9-zynq7000-zturn)	1m 15s
call-ci / build (armv7m4-stm32l4x6-nucleo)	1m 24s
call-ci / build (armv7m7-imxrt105x-evk)	1m 26s
call-ci / build (armv7m7-imxrt106x-evk)	1m 15s
call-ci / build (armv7m7-imxrt117x-evk)	1m 11s
call-ci / build (armv8r52-mps3an536-qemu)	1m 9s
call-ci / build (armv8m33-mcxn94x-frdm)	1m 10s
call-ci / build (host-generic-pc)	58s
call-ci / build (ia32-generic-pc)	4m 25s
call-ci / build (ia32-generic-qemu)	4m 9s
call-ci / build (riscv64-generic-qemu)	1m 12s
call-ci / build (riscv64-generic-spike)	1m 0s
call-ci / build (sparcv8leon-generic-qemu)	57s
call-ci / build (sparcv8leon-gr712rc-board)	55s
call-ci / build (sparcv8leon-gr716-mimas)	58s
call-ci / build (sparcv8leon-gr716-mini)	53s
call-ci / test EMU (armv7a9-zynq7000-qemu)	8m 35s
call-ci / test HW (armv7a7-imx6ull-evk)	7m 50s
call-ci / test EMU (host-generic-pc)	52s
call-ci / test HW (armv7m7-imxrt106x-evk)	2m 39s
call-ci / test EMU (ia32-generic-qemu)	6m 38s
call-ci / test HW (armv7m7-imxrt117x-evk)	2m 30s
call-ci / test EMU (riscv64-generic-qemu)	5m 35s
call-ci / test HW (armv7a9-zynq7000-zedboard)	2m 24s
call-ci / test EMU (sparcv8leon-generic-qemu)	2m 48s
call-ci / test HW (armv7m4-stm32l4x6-nucleo)	11m 30s
call-ci / tests-summary	21s
call-ci / send-notification	0s
	1h 22m 56s

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