Overlay on am33xx_pinmux: yocto enable overlays

for posterity sake, here are the values from my uboot of args_mmc_old and all the environment variables that are part of args_mmc_old

=> echo ${args_mmc_old}
setenv bootargs console=${console} ${optargs} ${cape_disable} ${cape_enable} ${cape_uboot} root=${oldroot} ro rootfstype=${mmcrootfstype} ${uboot_detected_capes} ${cmdline}
=> echo ${console}
ttyO0,115200n8
=> echo ${optargs}

=> echo ${cape_disable}

=> echo ${cape_enable}

=> echo ${cape_uboot}

=> echo ${oldroot}

=> echo ${mmcrootfstype}
ext4 rootwait
=> echo ${uboot_detected_capes}

=> echo ${cmdline}

=>