brcm47xx: rework model detection

brcm47xx: rework model detection

On brcm47xx boards, the model ID is the combination of the "boardtype" nvram
variable and an optional supplemental "boardnum" variable while the human
readable model name is usually exposed in the "machine" field of the
/proc/cpuinfo file.

Move the extraction of the board nvram variables and model name string into
the 01_sysinfo file and rework the 01_detect board configuration script to
solely use the prepared sysinfo values without performing own detection
logic.

As a consequence, we can drop the ucidef_set_board_id() and
ucidef_set_model_name() invocations in favor to the generic behaviour
which copies the /tmp/sysinfo/{board_name,model} values into the board.json
"id" and "name" fields respectively.

Since "01_detect" only contains network configuration logic after this
change, move it to "01_network" and rename the contained "detect_by_xxx"
functions to "configure_by_xxx" instead, to avoid potential confusion.

Fixes FS#1576
Acked-by: Rafał Miłecki <rafal@milecki.pl>
Signed-off-by: Jo-Philipp Wich <jo@mein.io>
(cherry picked from commit d7d10f2c1e8511fe07c9760e85f2272a85168f8d)