cmds: implement `mem` read/write tool #1034

Job	Run time
call-ci / build (armv7a7-imx6ull-evk)	1m 36s
call-ci / build (armv7a9-zynq7000-qemu)	1m 43s
call-ci / build (armv7a9-zynq7000-zedboard)	1m 12s
call-ci / build (armv7a9-zynq7000-zturn)	1m 22s
call-ci / build (armv7m4-stm32l4x6-nucleo)	1m 37s
call-ci / build (armv7m7-imxrt106x-evk)	2m 10s
call-ci / build (armv7m7-imxrt117x-evk)	1m 26s
call-ci / build (host-generic-pc)	1m 18s
call-ci / build (ia32-generic-pc)	1m 31s
call-ci / build (ia32-generic-qemu)	1m 19s
call-ci / build (riscv64-generic-qemu)	1m 7s
call-ci / build (riscv64-generic-spike)	1m 14s
call-ci / run tests on emulators (armv7a9-zynq7000-qemu)	19s
call-ci / run tests on emulators (host-generic-pc)	24s
call-ci / run tests on emulators (ia32-generic-qemu)	21s
call-ci / run tests on hardware (armv7a7-imx6ull-evk)	21s
call-ci / run tests on hardware (armv7m7-imxrt106x-evk)	31s
call-ci / run tests on hardware (armv7m7-imxrt117x-evk)	15s
call-ci / run tests on hardware (armv7a9-zynq7000-zedboard)	17s
call-ci / run tests on hardware (armv7m4-stm32l4x6-nucleo)	15s
call-ci / notify ci team using e-mail	2s
	20m 20s

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