embedded: Use blconfig alias to find bootloader config

[tdewey-rpi]

Use the blconfig alias to find the correct nvmem device to read the bootloader configuration, the practical effect being that IMAGER_REPO_URL should work on Raspberry Pi 5.

Fixes #894

[lurch]

@tdewey-rpi Comparing this to the https://github.com/raspberrypi/rpi-eeprom/blob/master/rpi-eeprom-update#L117 that @timg236 linked to in #894 , it looks like your're doing the

local blconfig_alias="/sys/firmware/devicetree/base/aliases/blconfig"

and

local blconfig_ofnode_link=$(find -L /sys/bus/nvmem -maxdepth 3 -samefile "${blconfig_ofnode_path}" 2>/dev/null)

parts, but you seem to be missing out the

local blconfig_ofnode_path="/sys/firmware/devicetree/base"$(strings "${blconfig_alias}")""

part in the middle? 🤔