fix: read BASE_BOARD from config before generate EXTRA_BOARD_CONFIG

[meteyou]

This PR fix the generate EXTRA_BOARD_CONFIG, because this was generated before CustomPiOS reads the config file. This is needed to build images which are not armhf, because generate_board_config.py has a fallback to raspberrypi os 32 bit with armhf, this override the BASE_ARCH with the EXTRA_BOARD_CONFIG.

This PR is based of the discussion from #240 and fixes #239

[guysoft]

Yes this looks like a better solution to this than #240
Will test on my end, and merge.

@jxmx Does this solve your issue in #240 ?

[guysoft]

Getting with this

 + tee build.log
 ++++ realpath -s /CustomPiOS/build
 +++ dirname /CustomPiOS/build
 ++ CUSTOM_OS_PATH=/CustomPiOS
 ++ CONFIG_FILE=/CustomPiOS/config
 ++ '[' -f /CustomPiOS/config ']'
 +++ bash -c 'source "/CustomPiOS/config" >/dev/null 2>&1; echo $BASE_BOARD'
 ++ BASE_BOARD_FROM_CONFIG=raspberrypiarmhf
 ++ '[' -n raspberrypiarmhf ']'
 ++ export BASE_BOARD=raspberrypiarmhf
 ++ BASE_BOARD=raspberrypiarmhf
 ++ echo 'BASE_BOARD set to raspberrypiarmhf from /CustomPiOS/config before generating board config.'
 BASE_BOARD set to raspberrypiarmhf from /CustomPiOS/config before generating board config.
 +++ mktemp
 ++ export EXTRA_BOARD_CONFIG=/tmp/tmp.zu4QyU1lSZ
 ++ EXTRA_BOARD_CONFIG=/tmp/tmp.zu4QyU1lSZ
 ++ /custompios_core/generate_board_config.py /tmp/tmp.zu4QyU1lSZ
 /CustomPiOS/build: line 59: /custompios_core/generate_board_config.py: No such file or directory
 + exit 1
 + chmod 777 /mnt/sda1/PleromaPi/src/workspace /mnt/sda1/PleromaPi/src/workspace-raspios_lite_arm64

Need to investigate more. Looks like its picking up the config file in CustomPiOS and not the config file in the distribution file

[guysoft]

Nope, on second thought #240 is better, its importing the correct distro config path and not custompios path